research on water

November 30, 2023

Traversing the waterways

In their anniversary editorial, Editors-in-Chief Jenna Davis and Pierre Horwitz and Executive Editor Debora Walker reflect on PLOS Water' s first year and their hopes and expectations for the future.

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Collection: Safe and Sustainable Water in Cities

This collection features articles that contribute new insights to the theme of fresh water in cities..

Water use and management

Water sovereignty for Indigenous Peoples: Pathways to pluralist, legitimate and sustainable water laws in settler colonial states

In this Review, Erin O’Donnell discusses how challenging false assumption of aqua nullius creates novel pathways for reform, enabling pluralist water laws and water governance models that improve both legitimacy and sustainability of settler state water governance.

Image credit: Drop of Water, by ronymichaud, Pixabay License

governance, policy, and politics

Putting diplomacy at the forefront of Water Diplomacy

In this Review, Hussein and colleagues stress the need to emphasize diplomacy and the goals beyond the water field in transboundary water governance. 

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water use and management

Safe and sustainable water in cities

In this Editorial, Narayan and Davis introduce our latest Collection and take a look at the themes that emerged as worthy research priorities for the urban water community.

Image credit: Tokyo by Telophase, Pixabay

Analysis of Microcystis aeruginosa physiology by spectral flow cytometry: Impact of chemical and light exposure

Brentjens and colleagues examined the impact of H2O2 and light stress on harmful algal bloom-forming cyanobacteria fluorescence using flow cytometry.

Image credit: cyanobacteria by armennano, Pixabay

Health IMPACTS AND SANITATION

A tale of two communities: Comparing user perceptions of condominial and conventional sewer systems in Salvador, Brazil

Palma and colleagues compare user perceptions of sewer systems in two communities in Brazil to inform implementation and long-term sustainability.

Image credit: Sewer Cover, by knavilio, Pixabay License

SOCIAL, CULTURAL, AND BEHAVIOURAL RESEARCH

Nature based solutions for flood risks: What insights do the social representations of experts provide?

Brueder and colleagues consider solutions for flood risks in the context of social representations

Image credit: Breuder et al., CC BY 4.0

Equity AND JUSTICE

Key mechanisms of a gender and socially inclusive community engagement and participatory design approach in the RISE program in Makassar, Indonesia and Suva, Fiji

Francis and colleagues identify mechanisms for engaging diverse residents in safe water access and management programs such as ‘RISE’

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WATER RESOURCES AND HYDROLOGY

Irish surface water response to the 2018 drought

Image credit: Smith et al., cc BY 4.0

WATER AND WASTE WATER TREATMENT

How do water matrices influence QSPR models in wastewater treatment?–A case study on the sonolytic elimination of phenol derivates

Image credit: Glienke et al., CC BY 4.0

Spatiotemporal trends in particle-associated microbial communities in a chlorinated drinking water distribution system

Image credit: Ferrebee et al., CC BY 4.0

WATER AND HYDROLOGY

Improved urban runoff prediction using high-resolution land-use, imperviousness, and stormwater infrastructure data applied to a process-based ecohydrological model

Image credit: Halama et al., CC BY 4.0

Safe and Sustainable Water in Cities

World water day 2023 – accelerating change, explore the latest research making an impact in your field, applying inclusive authorship criteria: two examples from plos water, river restoration, special collection for the 2023 unc water and health conference: science, policy and practice, publish with plos.

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Research on reclaimed water from the past to the future: a review

• Published: 08 May 2021
• Volume 24 , pages 112–137, ( 2022 )

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• Xun Li 1 &
• Yang Li 1  

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Reclaimed water is an important alternative water supply because it solves the water shortage problem. This manuscript is intended to provide a critical review of recent publications that address future reclaimed water requirements and analyze and visualize historical trends, research hot topics and promising future research directions. The results show that treatment technologies and optimized system designs for reclaimed water were early topics of interest. However, in the current era, "climate change," "sustainability," "technology," "impact" and other keywords appear frequently as the hot topics. Specifically, emerging research topics include (1) the influence of climate change on water quality and water supply system optimization under uncertainty, (2) improving public acceptance and strengthening water management and policy implementation, (3) developing and applying cost-effective treatment technologies for the removal of trace pollutants and (4) more comprehensive health risk assessment and online detection technology. This analysis accurately reflects historical trends in the field and will help researchers choose future research topics.

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Reclaimed Water

Water Pollution and Treatment Technologies

Decision making for implementing non-traditional water sources: a review of challenges and potential solutions

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Acknowledgements

This work was supported by the National Science Foundation of China [Grant No.51409189]; Training Program for Innovative Research Team in Tianjin Institutions of Higher Education [TD13-5021]; and Tianjin Key Laboratory of Hazardous Waste Safety Disposal and Recycling Technology. The authors also thank the reviewers for their detailed comments.

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Li, X., Li, X. & Li, Y. Research on reclaimed water from the past to the future: a review. Environ Dev Sustain 24 , 112–137 (2022). https://doi.org/10.1007/s10668-021-01495-w

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DOI : https://doi.org/10.1007/s10668-021-01495-w

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There are many options for what to drink , but water is the best choice for most people who have access to safe drinking water. It is calorie-free and as easy to find as the nearest tap.

Water helps to restore fluids lost through metabolism, breathing, sweating, and the removal of waste. It helps to keep you from overheating, lubricates the joints and tissues, maintains healthy skin, and is necessary for proper digestion. It’s the perfect zero-calorie beverage for quenching thirst and rehydrating your body.

How Much Water Do I Need?

Water is an essential nutrient at every age, so optimal hydration is a key component for good health. Water accounts for about 60% of an adult’s body weight. We drink fluids when we feel thirst, the major signal alerting us when our body runs low on water. We also customarily drink beverages with meals to help with digestion. But sometimes we drink not based on these factors but on how much we think we should be drinking. One of the most familiar sayings is to aim for “8 glasses a day,” but this may not be appropriate for every person.

General recommendations

• The National Academy of Medicine suggests an adequate intake of daily fluids of about 13 cups and 9 cups for healthy men and women, respectively, with 1 cup equaling 8 ounces. [1] Higher amounts may be needed for those who are physically active or exposed to very warm climates. Lower amounts may be needed for those with smaller body sizes. It’s important to note that this amount is not a daily target, but a general guide. In the average person, drinking less will not necessarily compromise one’s health as each person’s exact fluid needs vary, even day-to-day.
• Fever, exercise, exposure to extreme temperature climates (very hot or cold), and excessive loss of body fluids (such as with vomiting or diarrhea) will increase fluid needs.
• The amount and color of urine can provide a rough estimate of adequate hydration. Generally the color of urine darkens the more concentrated it is (meaning that it contains less water). However, foods, medications, and vitamin supplements can also change urine color. [1] Smaller volumes of urine may indicate dehydration, especially if also darker in color.
• Alcohol can suppress anti-diuretic hormone, a fluid-regulating hormone that signals the kidneys to reduce urination and reabsorb water back into the body. Without it, the body flushes out water more easily. Enjoying more than a couple of drinks within a short time can increase the risk of dehydration, especially if taken on an empty stomach. To prevent this, take alcohol with food and sips of water.
• Although caffeine has long been thought to have a diuretic effect, potentially leading to dehydration, research does not fully support this. The data suggest that more than 180 mg of caffeine daily (about two cups of brewed coffee) may increase urination in the short-term in some people, but will not necessarily lead to dehydration. Therefore, caffeinated beverages including coffee and tea can contribute to total daily water intake. [1]

Keep in mind that about 20% of our total water intake comes not from beverages but from water-rich foods like lettuce, leafy greens, cucumbers, bell peppers, summer squash, celery, berries, and melons.

Aside from including water-rich foods, the following chart is a guide for daily water intake based on age group from the National Academy of Medicine:

Preventing Dehydration: Is Thirst Enough?

As we age, however, the body’s regulation of fluid intake and thirst decline. Research has shown that both of these factors are impaired in the elderly. A Cochrane review found that commonly used indicators of dehydration in older adults (e.g., urine color and volume, feeling thirsty) are not effective and should not be solely used. [3] Certain conditions that impair mental ability and cognition, such as a stroke or dementia, can also impair thirst. People may also voluntarily limit drinking due to incontinence or difficulty getting to a bathroom. In addition to these situations, research has found that athletes, people who are ill, and infants may not have an adequate sense of thirst to replete their fluid needs. [2] Even mild dehydration may produce negative symptoms, so people who cannot rely on thirst or other usual measures may wish to use other strategies. For example, aim to fill a 20-ounce water bottle four times daily and sip throughout the day, or drink a large glass of water with each meal and snack.

Symptoms of dehydration that may occur with as little as a 2% water deficit:

• Confusion or short-term memory loss
• Mood changes like increased irritability or depression

Dehydration can increase the risk of certain medical conditions:

• Urinary tract infections
• Kidney stones
• Constipation  

Like most trends of the moment, alkaline water has become popular through celebrity backing with claims ranging from weight loss to curing cancer. The theory behind alkaline water is the same as that touting the benefits of eating alkaline foods, which purportedly counterbalances the health detriments caused by eating acid-producing foods like meat, sugar, and some grains.

From a scale of 0-14, a higher pH number is alkaline; a lower pH is acidic. The body tightly regulates blood pH levels to about 7.4 because veering away from this number to either extreme can cause negative side effects and even be life-threatening. However, diet alone cannot cause these extremes; they most commonly occur with conditions like uncontrolled diabetes, kidney disease, chronic lung disease, or alcohol abuse.

Alkaline water has a higher pH of about 8-9 than tap water of about 7, due to a higher mineral or salt content. Some water sources can be naturally alkaline if the water picks up minerals as it passes over rocks. However, most commercial brands of alkaline water have been manufactured using an ionizer that reportedly separates out the alkaline components and filters out the acid components, raising the pH. Some people add an alkaline substance like baking soda to regular water.

Scientific evidence is not conclusive on the acid-alkaline theory, also called the acid-ash theory, stating that eating a high amount of certain foods can slightly lower the pH of blood especially in the absence of eating foods supporting a higher alkaline blood pH like fruits, vegetables, and legumes. Controlled clinical trials have not shown that diet alone can significantly change the blood pH of healthy people. Moreover, a direct connection of blood pH in the low-normal range and chronic disease in humans has not been established.

BOTTOM LINE: If the idea of alkaline water encourages you to drink more, then go for it! But it’s likely that drinking plain regular water will provide similar health benefits from simply being well-hydrated—improved energy, mood, and digestive health

Is It Possible To Drink Too Much Water?

There is no Tolerable Upper Intake Level for water because the body can usually excrete extra water through urine or sweat. However, a condition called water toxicity is possible in rare cases, in which a large amount of fluids is taken in a short amount of time, which is faster than the kidney’s ability to excrete it. This leads to a dangerous condition called hyponatremia in which blood levels of sodium fall too low as too much water is taken. The excess total body water dilutes blood sodium levels, which can cause symptoms like confusion, nausea, seizures, and muscle spasms. Hyponatremia is usually only seen in ill people whose kidneys are not functioning properly or under conditions of extreme heat stress or prolonged strenuous exercise where the body cannot excrete the extra water. Very physically active people such as triathletes and marathon runners are at risk for this condition as they tend to drink large amounts of water, while simultaneously losing sodium through their sweat. Women and children are also more susceptible to hyponatremia because of their smaller body size.

Fun Flavors For Water  

Infused water

Instead of purchasing expensive flavored waters in the grocery store, you can easily make your own at home. Try adding any of the following to a cold glass or pitcher of water:

• Sliced citrus fruits or zest (lemon, lime, orange, grapefruit)
• Crushed fresh mint
• Peeled, sliced fresh ginger or sliced cucumber
• Crushed berries

Sparkling water with a splash of juice

Sparkling juices may have as many calories as sugary soda. Instead, make your own sparkling juice at home with 12 ounces of sparkling water and just an ounce or two of juice. For additional flavor, add sliced citrus or fresh herbs like mint.

TIP: To reduce waste, reconsider relying on single-use plastic water bottles and purchase a colorful 20-32 ounce refillable water thermos that is easy to wash and tote with you during the day. 

Are seltzers and other fizzy waters safe and healthy to drink?

BOTTOM LINE: Carbonated waters, if unsweetened, are safe to drink and a good beverage choice. They are not associated with health problems that are linked with sweetened, carbonated beverages like soda.

• Harvard T.H. Chan School of Public Health is a member of the Nutrition and Obesity Policy Research and Evaluation Network’s (NOPREN) Drinking Water Working Group. A collaborative network of the Centers for Disease Control and Prevention, the NOPREN Drinking Water Working Group focuses on policies and economic issues regarding free and safe drinking water access in various settings by conducting research and evaluation to help identify, develop and implement drinking-water-related policies, programs, and practices. Visit the network’s website to access recent water research and evidence-based resources.
• The Harvard Prevention Research Center on Nutrition and Physical Activity provides tools and resources for making clean, cold, free water more accessible in environments like schools and afterschool programs, as well as tips for making water more tasty and fun for kids.
• The National Academy of Sciences. Dietary References Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. https://www.nap.edu/read/10925/chapter/6#102 Accessed 8/5/2019.
• Millard-Stafford M, Wendland DM, O’Dea NK, Norman TL. Thirst and hydration status in everyday life. Nutr Rev . 2012 Nov;70 Suppl 2:S147-51.
• Hooper L, Abdelhamid A, Attreed NJ, Campbell WW, Channell AM, et al. Clinical symptoms, signs and tests for identification of impending and current water-loss dehydration in older people. Cochrane Database Syst Rev . 2015 Apr 30;(4):CD009647.

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Article Contents

Introduction, physiological effects of dehydration, hydration and chronic diseases, water consumption and requirements and relationships to total energy intake, water requirements: evaluation of the adequacy of water intake, acknowledgments, water, hydration, and health.

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Barry M Popkin, Kristen E D'Anci, Irwin H Rosenberg, Water, hydration, and health, Nutrition Reviews , Volume 68, Issue 8, 1 August 2010, Pages 439–458, https://doi.org/10.1111/j.1753-4887.2010.00304.x

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This review examines the current knowledge of water intake as it pertains to human health, including overall patterns of intake and some factors linked with intake, the complex mechanisms behind water homeostasis, and the effects of variation in water intake on health and energy intake, weight, and human performance and functioning. Water represents a critical nutrient, the absence of which will be lethal within days. Water's importance for the prevention of nutrition-related noncommunicable diseases has received more attention recently because of the shift toward consumption of large proportions of fluids as caloric beverages. Despite this focus, there are major gaps in knowledge related to the measurement of total fluid intake and hydration status at the population level; there are also few longer-term systematic interventions and no published randomized, controlled longer-term trials. This review provides suggestions for ways to examine water requirements and encourages more dialogue on this important topic.

Water is essential for life. From the time that primeval species ventured from the oceans to live on land, a major key to survival has been the prevention of dehydration. The critical adaptations cross an array of species, including man. Without water, humans can survive only for days. Water comprises from 75% body weight in infants to 55% in the elderly and is essential for cellular homeostasis and life. 1 Nevertheless, there are many unanswered questions about this most essential component of our body and our diet. This review attempts to provide some sense of our current knowledge of water, including overall patterns of intake and some factors linked with intake, the complex mechanisms behind water homeostasis, the effects of variation in water intake on health and energy intake, weight, and human performance and functioning.

Recent statements on water requirements have been based on retrospective recall of water intake from food and beverages among healthy, noninstitutionalized individuals. Provided here are examples of water intake assessment in populations to clarify the need for experimental studies. Beyond these circumstances of dehydration, it is not fully understood how hydration affects health and well-being, even the impact of water intakes on chronic diseases. Recently, Jéquier and Constant 2 addressed this question based on human physiology, but more knowledge is required about the extent to which water intake might be important for disease prevention and health promotion.

As noted later in the text, few countries have developed water requirements and those that exist are based on weak population-level measures of water intake and urine osmolality. 3 , 4 The European Food Safety Authority (EFSA) was recently asked to revise existing recommended intakes of essential substances with a physiological effect, including water since this nutrient is essential for life and health. 5

The US Dietary Recommendations for water are based on median water intakes with no use of measurements of the dehydration status of the population to assist. One-time collection of blood samples for the analysis of serum osmolality has been used by the National Health and Nutrition Examination Survey program. At the population level, there is no accepted method of assessing hydration status, and one measure some scholars use, hypertonicity, is not even linked with hydration in the same direction for all age groups. 6 Urine indices are used often but these reflect the recent volume of fluid consumed rather than a state of hydration. 7 Many scholars use urine osmolality to measure recent hydration status. 8 , – 12 Deuterium dilution techniques (isotopic dilution with D 2 O, or deuterium oxide) allow measurement of total body water but not water balance status. 13 Currently, there are no completely adequate biomarkers to measure hydration status at the population level.

In discussing water, the focus is first and foremost on all types of water, whether it be soft or hard, spring or well, carbonated or distilled. Furthermore, water is not only consumed directly as a beverage; it is also obtained from food and to a very small extent from oxidation of macronutrients (metabolic water). The proportion of water that comes from beverages and food varies according to the proportion of fruits and vegetables in the diet. The ranges of water content in various foods are presented in Table 1 . In the United States it is estimated that about 22% of water intake comes from food while the percentages are much higher in European countries, particularly a country like Greece with its higher intake of fruits and vegetables, or in South Korea. 3 , – 15 The only in-depth study performed in the United States of water use and water intrinsic to food found a 20.7% contribution from food water; 16 , 17 however, as shown below, this research was dependent on poor overall assessment of water intake.

Ranges of water content for selected foods.

Data from the USDA national nutrient database for standard reference, release 21, as provided in Altman. 126

This review considers water requirements in the context of recent efforts to assess water intake in US populations. The relationship between water and calorie intake is explored both for insights into the possible displacement of calories from sweetened beverages by water and to examine the possibility that water requirements would be better expressed in relation to calorie/energy requirements with the dependence of the latter on age, size, gender, and physical activity level. Current understanding of the exquisitely complex and sensitive system that protects land animals against dehydration is covered and commentary is provided on the complications of acute and chronic dehydration in man, against which a better expression of water requirements might complement the physiological control of thirst. Indeed, the fine intrinsic regulation of hydration and water intake in individuals mitigates prevalent underhydration in populations and its effects on function and disease.

Regulation of fluid intake

To prevent dehydration, reptiles, birds, vertebrates, and all land animals have evolved an exquisitely sensitive network of physiological controls to maintain body water and fluid intake by thirst. Humans may drink for various reasons, particularly for hedonic ones, but drinking is most often due to water deficiency that triggers the so-called regulatory or physiological thirst. The mechanism of thirst is quite well understood today and the reason nonregulatory drinking is often encountered is related to the large capacity of the kidneys to rapidly eliminate excesses of water or to reduce urine secretion to temporarily economize on water. 1 But this excretory process can only postpone the necessity of drinking or of ceasing to drink an excess of water. Nonregulatory drinking is often confusing, particularly in wealthy societies that have highly palatable drinks or fluids that contain other substances the drinker seeks. The most common of these are sweeteners or alcohol for which water is used as a vehicle. Drinking these beverages is not due to excessive thirst or hyperdipsia, as can be shown by offering pure water to individuals instead and finding out that the same drinker is in fact hypodipsic (characterized by abnormally diminished thirst). 1

Fluid balance of the two compartments

Maintaining a constant water and mineral balance requires the coordination of sensitive detectors at different sites in the body linked by neural pathways with integrative centers in the brain that process this information. These centers are also sensitive to humoral factors (neurohormones) produced for the adjustment of diuresis, natriuresis, and blood pressure (angiotensin mineralocorticoids, vasopressin, atrial natriuretic factor). Instructions from the integrative centers to the “executive organs” (kidney, sweat glands, and salivary glands) and to the part of the brain responsible for corrective actions such as drinking are conveyed by certain nerves in addition to the above-mentioned substances. 1

Most of the components of fluid balance are controlled by homeostatic mechanisms responding to the state of body water. These mechanisms are sensitive and precise, and are activated with deficits or excesses of water amounting to only a few hundred milliliters. A water deficit produces an increase in the ionic concentration of the extracellular compartment, which takes water from the intracellular compartment causing cells to shrink. This shrinkage is detected by two types of brain sensors, one controlling drinking and the other controlling the excretion of urine by sending a message to the kidneys, mainly via the antidiuretic hormone vasopressin to produce a smaller volume of more concentrated urine. 18 When the body contains an excess of water, the reverse processes occur: the lower ionic concentration of body fluids allows more water to reach the intracellular compartment. The cells imbibe, drinking is inhibited, and the kidneys excrete more water.

The kidneys thus play a key role in regulating fluid balance. As discussed later, the kidneys function more efficiently in the presence of an abundant water supply. If the kidneys economize on water and produce more concentrated urine, they expend a greater amount of energy and incur more wear on their tissues. This is especially likely to occur when the kidneys are under stress, e.g., when the diet contains excessive amounts of salt or toxic substances that need to be eliminated. Consequently, drinking a sufficient amount of water helps protect this vital organ.

Regulatory drinking

Most drinking occurs in response to signals of water deficit. Apart from urinary excretion, the other main fluid regulatory process is drinking, which is mediated through the sensation of thirst. There are two distinct mechanisms of physiological thirst: the intracellular and the extracellular mechanisms. When water alone is lost, ionic concentration increases. As a result, the intracellular space yields some of its water to the extracellular compartment. Once again, the resulting shrinkage of cells is detected by brain receptors that send hormonal messages to induce drinking. This association with receptors that govern extracellular volume is accompanied by an enhancement of appetite for salt. Thus, people who have been sweating copiously prefer drinks that are relatively rich in Na+ salts rather than pure water. When excessive sweating is experienced, it is also important to supplement drinks with additional salt.

The brain's decision to start or stop drinking and to choose the appropriate drink is made before the ingested fluid can reach the intra- and extracellular compartments. The taste buds in the mouth send messages to the brain about the nature, and especially the salt content, of the ingested fluid, and neuronal responses are triggered as if the incoming water had already reached the bloodstream. These are the so-called anticipatory reflexes: they cannot be entirely “cephalic reflexes” because they arise from the gut as well as the mouth. 1

The anterior hypothalamus and pre-optic area are equipped with osmoreceptors related to drinking. Neurons in these regions show enhanced firing when the inner milieu gets hyperosmotic. Their firing decreases when water is loaded in the carotid artery that irrigates the neurons. It is remarkable that the same decrease in firing in the same neurons takes place when the water load is applied on the tongue instead of being injected into the carotid artery. This anticipatory drop in firing is due to communication from neural pathways that depart from the mouth and converge onto neurons that simultaneously sense the blood's inner milieu.

Nonregulatory drinking

Although everyone experiences thirst from time to time, it plays little role in the day-to-day control of water intake in healthy people living in temperate climates. In these regions, people generally consume fluids not to quench thirst, but as components of everyday foods (e.g., soup, milk), as beverages used as mild stimulants (tea, coffee), and for pure pleasure. A common example is alcohol consumption, which can increase individual pleasure and stimulate social interaction. Drinks are also consumed for their energy content, as in soft drinks and milk, and are used in warm weather for cooling and in cold weather for warming. Such drinking seems to also be mediated through the taste buds, which communicate with the brain in a kind of “reward system”, the mechanisms of which are just beginning to be understood. This bias in the way human beings rehydrate themselves may be advantageous because it allows water losses to be replaced before thirst-producing dehydration takes place. Unfortunately, this bias also carries some disadvantages. Drinking fluids other than water can contribute to an intake of caloric nutrients in excess of requirements, or in alcohol consumption that, in some people, may insidiously bring about dependence. For example, total fluid intake increased from 79 fluid ounces in 1989 to 100 fluid ounces in 2002 among US adults, with the difference representing intake of caloric beverages. 19

Effects of aging on fluid intake regulation

The thirst and fluid ingestion responses of older persons to a number of stimuli have been compared to those of younger persons. 20 Following water deprivation, older individuals are less thirsty and drink less fluid compared to younger persons. 21 , 22 The decrease in fluid consumption is predominantly due to a decrease in thirst, as the relationship between thirst and fluid intake is the same in young and old persons. Older persons drink insufficient amounts of water following fluid deprivation to replenish their body water deficit. 23 When dehydrated older persons are offered a highly palatable selection of drinks, this also fails to result in increased fluid intake. 23 The effects of increased thirst in response to an osmotic load have yielded variable responses, with one group reporting reduced osmotic thirst in older individuals 24 and one failing to find a difference. In a third study, young individuals ingested almost twice as much fluid as old persons, even though the older subjects had a much higher serum osmolality. 25

Overall, these studies support small changes in the regulation of thirst and fluid intake with aging. Defects in both osmoreceptors and baroreceptors appear to exist as do changes in the central regulatory mechanisms mediated by opioid receptors. 26 Because the elderly have low water reserves, it may be prudent for them to learn to drink regularly when not thirsty and to moderately increase their salt intake when they sweat. Better education on these principles may help prevent sudden hypotension and stroke or abnormal fatigue, which can lead to a vicious circle and eventually hospitalization.

Thermoregulation

Hydration status is critical to the body's process of temperature control. Body water loss through sweat is an important cooling mechanism in hot climates and in periods of physical activity. Sweat production is dependent upon environmental temperature and humidity, activity levels, and type of clothing worn. Water losses via skin (both insensible perspiration and sweating) can range from 0.3 L/h in sedentary conditions to 2.0 L/h in high activity in the heat, and intake requirements range from 2.5 to just over 3 L/day in adults under normal conditions, and can reach 6 L/day with high extremes of heat and activity. 27 , 28 Evaporation of sweat from the body results in cooling of the skin. However, if sweat loss is not compensated for with fluid intake, especially during vigorous physical activity, a hypohydrated state can occur with concomitant increases in core body temperature. Hypohydration from sweating results in a loss of electrolytes, as well as a reduction in plasma volume, and this can lead to increased plasma osmolality. During this state of reduced plasma volume and increased plasma osmolality, sweat output becomes insufficient to offset increases in core temperature. When fluids are given to maintain euhydration, sweating remains an effective compensation for increased core temperatures. With repeated exposure to hot environments, the body adapts to heat stress and cardiac output and stroke volume return to normal, sodium loss is conserved, and the risk for heat-stress-related illness is reduced. 29 Increasing water intake during this process of heat acclimatization will not shorten the time needed to adapt to the heat, but mild dehydration during this time may be of concern and is associated with elevations in cortisol, increased sweating, and electrolyte imbalances. 29

Children and the elderly have differing responses to ambient temperature and different thermoregulatory concerns than healthy adults. Children in warm climates may be more susceptible to heat illness than adults due to their greater surface area to body mass ratio, lower rate of sweating, and slower rate of acclimatization to heat. 30 , 31 Children may respond to hypohydration during activity with a higher relative increase in core temperature than adults, 32 and with a lower propensity to sweat, thus losing some of the benefits of evaporative cooling. However, it has been argued that children can dissipate a greater proportion of body heat via dry heat loss, and the concomitant lack of sweating provides a beneficial means of conserving water under heat stress. 30 Elders, in response to cold stress, show impairments in thermoregulatory vasoconstriction, and body water is shunted from plasma into the interstitial and intracellular compartments. 33 , 34 With respect to heat stress, water lost through sweating decreases the water content of plasma, and the elderly are less able to compensate for increased blood viscosity. 33 Not only do they have a physiological hypodipsia, but this can be exaggerated by central nervous system disease 35 and by dementia. 36 In addition, illness and limitations in daily living activities can further limit fluid intake. When reduced fluid intake is coupled with advancing age, there is a decrease in total body water. Older individuals have impaired renal fluid conservation mechanisms and, as noted above, have impaired responses to heat and cold stress. 33 , 34 All of these factors contribute to an increased risk of hypohydration and dehydration in the elderly.

With regard to physiology, the role of water in health is generally characterized in terms of deviations from an ideal hydrated state, generally in comparison to dehydration. The concept of dehydration encompasses both the process of losing body water and the state of dehydration. Much of the research on water and physical or mental functioning compares a euhydrated state, usually achieved by provision of water sufficient to overcome water loss, to a dehydrated state, which is achieved via withholding of fluids over time and during periods of heat stress or high activity. In general, provision of water is beneficial in individuals with a water deficit, but little research supports the notion that additional water in adequately hydrated individuals confers any benefit.

Physical performance

The role of water and hydration in physical activity, particularly in athletes and in the military, has been of considerable interest and is well-described in the scientific literature. 37 , – 39 During challenging athletic events, it is not uncommon for athletes to lose 6–10% of body weight through sweat, thus leading to dehydration if fluids have not been replenished. However, decrements in the physical performance of athletes have been observed under much lower levels of dehydration, i.e., as little as 2%. 38 Under relatively mild levels of dehydration, individuals engaging in rigorous physical activity will experience decrements in performance related to reduced endurance, increased fatigue, altered thermoregulatory capability, reduced motivation, and increased perceived effort. 40 , 41 Rehydration can reverse these deficits and reduce the oxidative stress induced by exercise and dehydration. 42 Hypohydration appears to have a more significant impact on high-intensity and endurance activity, such as tennis 43 and long-distance running, 44 than on anaerobic activities, 45 such as weight lifting, or on shorter-duration activities, such as rowing. 46

During exercise, individuals may not hydrate adequately when allowed to drink according to thirst. 32 After periods of physical exertion, voluntary fluid intake may be inadequate to offset fluid deficits. 1 Thus, mild-to-moderate dehydration can persist for some hours after the conclusion of physical activity. Research performed on athletes suggests that, principally at the beginning of the training season, they are at particular risk for dehydration due to lack of acclimatization to weather conditions or suddenly increased activity levels. 47 , 48 A number of studies show that performance in temperate and hot climates is affected to a greater degree than performance in cold temperatures. 41 , – 50 Exercise in hot conditions with inadequate fluid replacement is associated with hyperthermia, reduced stroke volume and cardiac output, decreases in blood pressure, and reduced blood flow to muscle. 51

During exercise, children may be at greater risk for voluntary dehydration. Children may not recognize the need to replace lost fluids, and both children as well as coaches need specific guidelines for fluid intake. 52 Additionally, children may require more time to acclimate to increases in environmental temperature than adults. 30 , 31 Recommendations are for child athletes or children in hot climates to begin athletic activities in a well-hydrated state and to drink fluids over and above the thirst threshold.

Cognitive performance

Water, or its lack (dehydration), can influence cognition. Mild levels of dehydration can produce disruptions in mood and cognitive functioning. This may be of special concern in the very young, very old, those in hot climates, and those engaging in vigorous exercise. Mild dehydration produces alterations in a number of important aspects of cognitive function such as concentration, alertness, and short-term memory in children (10–12 y), 32 young adults (18–25 y), 53 , – 56 and the oldest adults (50–82 y). 57 As with physical functioning, mild-to-moderate levels of dehydration can impair performance on tasks such as short-term memory, perceptual discrimination, arithmetic ability, visuomotor tracking, and psychomotor skills. 53 , – 56 However, mild dehydration does not appear to alter cognitive functioning in a consistent manner. 53 , – 58 In some cases, cognitive performance was not significantly affected in ranges from 2% to 2.6% dehydration. 56 , 58 Comparing across studies, performance on similar cognitive tests was divergent under dehydration conditions. 54 , 56 In studies conducted by Cian et al., 53 , 54 participants were dehydrated to approximately 2.8% either through heat exposure or treadmill exercise. In both studies, performance was impaired on tasks examining visual perception, short-term memory, and psychomotor ability. In a series of studies using exercise in conjunction with water restriction as a means of producing dehydration, D'Anci et al. 56 observed only mild decrements in cognitive performance in healthy young men and women athletes. In these experiments, the only consistent effect of mild dehydration was significant elevations of subjective mood score, including fatigue, confusion, anger, and vigor. Finally, in a study using water deprivation alone over a 24-h period, no significant decreases in cognitive performance were seen with 2.6% dehydration. 58 It is therefore possible that heat stress may play a critical role in the effects of dehydration on cognitive performance.

Reintroduction of fluids under conditions of mild dehydration can reasonably be expected to reverse dehydration-induced cognitive deficits. Few studies have examined how fluid reintroduction may alleviate the negative effects of dehydration on cognitive performance and mood. One study 59 examined how water ingestion affected arousal and cognitive performance in young people following a period of 12-h water restriction. While cognitive performance was not affected by either water restriction or water consumption, water ingestion affected self-reported arousal. Participants reported increased alertness as a function of water intake. Rogers et al. 60 observed a similar increase in alertness following water ingestion in both high- and low-thirst participants. Water ingestion, however, had opposite effects on cognitive performance as a function of thirst. High-thirst participants' performance on a cognitively demanding task improved following water ingestion, but low-thirst participants' performance declined. In summary, hydration status consistently affected self-reported alertness, but effects on cognition were less consistent.

Several recent studies have examined the utility of providing water to school children on attentiveness and cognitive functioning in children. 61 , – 63 In these experiments, children were not fluid restricted prior to cognitive testing, but were allowed to drink as usual. Children were then provided with a drink or no drink 20–45 min before the cognitive test sessions. In the absence of fluid restriction and without physiological measures of hydration status, the children in these studies should not be classified as dehydrated. Subjective measures of thirst were reduced in children given water, 62 and voluntary water intake in children varied from 57 mL to 250 mL. In these studies, as in the studies in adults, the findings were divergent and relatively modest. In the research led by Edmonds et al., 61 , 62 children in the groups given water showed improvements in visual attention. However, effects on visual memory were less consistent, with one study showing no effects of drinking water on a spot-the-difference task in 6–7-year-old children 61 and the other showing a significant improvement in a similar task in 7–9-year-old children. 62 In the research described by Benton and Burgess, 63 memory performance was improved by provision of water but sustained attention was not altered with provision of water in the same children.

Taken together, these studies indicate that low-to-moderate dehydration may alter cognitive performance. Rather than indicating that the effects of hydration or water ingestion on cognition are contradictory, many of the studies differ significantly in methodology and in measurement of cognitive behaviors. These variances in methodology underscore the importance of consistency when examining relatively subtle chances in overall cognitive performance. However, in those studies in which dehydration was induced, most combined heat and exercise; this makes it difficult to disentangle the effects of dehydration on cognitive performance in temperate conditions from the effects of heat and exercise. Additionally, relatively little is known about the mechanism of mild dehydration's effects on mental performance. It has been proposed that mild dehydration acts as a physiological stressor that competes with and draws attention from cognitive processes. 64 However, research on this hypothesis is limited and merits further exploration.

Dehydration and delirium

Dehydration is a risk factor for delirium and for delirium presenting as dementia in the elderly and in the very ill. 65 , – 67 Recent work shows that dehydration is one of several predisposing factors for confusion observed in long-term-care residents 67 ; however, in this study, daily water intake was used as a proxy measure for dehydration rather than other, more direct clinical assessments such as urine or plasma osmolality. Older people have been reported as having reduced thirst and hypodipsia relative to younger people. In addition, fluid intake and maintenance of water balance can be complicated by factors such as disease, dementia, incontinence, renal insufficiency, restricted mobility, and drug side effects. In response to primary dehydration, older people have less thirst sensation and reduced fluid intakes in comparison to younger people. However, in response to heat stress, while older people still display a reduced thirst threshold, they do ingest comparable amounts of fluid to younger people. 20

Gastrointestinal function

Fluids in the diet are generally absorbed in the proximal small intestine, and the absorption rate is determined by the rate of gastric emptying to the small intestine. Therefore, the total volume of fluid consumed will eventually be reflected in water balance, but the rate at which rehydration occurs is dependent upon factors affecting the rate of delivery of fluids to the intestinal mucosa. The gastric emptying rate is generally accelerated by the total volume consumed and slowed by higher energy density and osmolality. 68 In addition to water consumed in food (1 L/day) and beverages (circa 2–3 L/day), digestive secretions account for a far greater portion of water that passes through and is absorbed by the gastrointestinal tract (circa 8 L/day). 69 The majority of this water is absorbed by the small intestine, with a capacity of up to 15 L/day with the colon absorbing some 5 L/day. 69

Constipation, characterized by slow gastrointestinal transit, small, hard stools, and difficulty in passing stool, has a number of causes, including medication use, inadequate fiber intake, poor diet, and illness. 70 Inadequate fluid consumption is touted as a common culprit in constipation, and increasing fluid intake is a frequently recommended treatment. Evidence suggests, however, that increasing fluids is only useful to individuals in a hypohydrated state, and is of little utility in euhydrated individuals. 70 In young children with chronic constipation, increasing daily water intake by 50% did not affect constipation scores. 71 For Japanese women with low fiber intake, concomitant low water intake in the diet is associated with increased prevalence of constipation. 72 In older individuals, low fluid intake is a predictor for increased levels of acute constipation, 73 , 74 with those consuming the least amount of fluid having over twice the frequency of constipation episodes than those consuming the most fluid. In one trial, researchers compared the utility of carbonated mineral water in reducing functional dyspepsia and constipation scores to tap water in individuals with functional dyspepsia. 75 When comparing carbonated mineral water to tap water, participants reported improvements in subjective gastric symptoms, but there were no significant improvements in gastric or intestinal function. The authors indicate it is not possible to determine to what degree the mineral content of the two waters contributed to perceived symptom relief, as the mineral water contained greater levels of magnesium and calcium than the tap water. The available evidence suggests that increased fluid intake should only be indicated in individuals in a hypohydrated state. 69 , 71

Significant water loss can occur through the gastrointestinal tract, and this can be of great concern in the very young. In developing countries, diarrheal diseases are a leading cause of death in children, resulting in approximately 1.5–2.5 million deaths per year. 76 Diarrheal illness results not only in a reduction in body water, but also in potentially lethal electrolyte imbalances. Mortality in such cases can many times be prevented with appropriate oral rehydration therapy, by which simple dilute solutions of salt and sugar in water can replace fluid lost by diarrhea. Many consider application of oral rehydration therapy to be one of the significant public health developments of the last century. 77

Kidney function

As noted above, the kidney is crucial in regulating water balance and blood pressure as well as removing waste from the body. Water metabolism by the kidney can be classified into regulated and obligate. Water regulation is hormonally mediated, with the goal of maintaining a tight range of plasma osmolality (between 275 and 290 mOsm/kg). Increases in plasma osmolality and activation of osmoreceptors (intracellular) and baroreceptors (extracellular) stimulate hypothalamic release of arginine vasopressin (AVP). AVP acts at the kidney to decrease urine volume and promote retention of water, and the urine becomes hypertonic. With decreased plasma osmolality, vasopressin release is inhibited, and the kidney increases hypotonic urinary output.

In addition to regulating fluid balance, the kidneys require water for the filtration of waste from the bloodstream and excretion via urine. Water excretion via the kidney removes solutes from the blood, and a minimum obligate urine volume is required to remove the solute load with a maximum output volume of 1 L/h. 78 This obligate volume is not fixed, but is dependent upon the amount of metabolic solutes to be excreted and levels of AVP. Depending on the need for water conservation, basal urine osmolality ranges from 40 mOsm/kg to a maximum of 1,400 mOsm/kg. 78 The ability to both concentrate and dilute urine decreases with age, with a lower value of 92 mOsm/kg and an upper range falling between 500 and 700 mOsm/kg for individuals over the age of 70 years. 79 , – 81 Under typical conditions, in an average adult, urine volume of 1.5 to 2.0 L/day would be sufficient to clear a solute load of 900 to 1,200 mOsm/day. During water conservation and the presence of AVP, this obligate volume can decrease to 0.75–1.0 L/day and during maximal diuresis up to 20 L/day can be required to remove the same solute load. 78 , – 81 In cases of water loading, if the volume of water ingested cannot be compensated for with urine output, having overloaded the kidney's maximal output rate, an individual can enter a hyponatremic state.

Heart function and hemodynamic response

Blood volume, blood pressure, and heart rate are closely linked. Blood volume is normally tightly regulated by matching water intake and water output, as described in the section on kidney function. In healthy individuals, slight changes in heart rate and vasoconstriction act to balance the effect of normal fluctuations in blood volume on blood pressure. 82 Decreases in blood volume can occur, through blood loss (or blood donation), or loss of body water through sweat, as seen with exercise. Blood volume is distributed differently relative to the position of the heart, whether supine or upright, and moving from one position to the other can lead to increased heart rate, a fall in blood pressure, and, in some cases, syncope. This postural hypotension (or orthostatic hypotension) can be mediated by drinking 300–500 mL of water. 83 , 84 Water intake acutely reduces heart rate and increases blood pressure in both normotensive and hypertensive individuals. 85 These effects of water intake on the pressor effect and heart rate occur within 15–20 min of drinking water and can last for up to 60 min. Water ingestion is also beneficial in preventing vasovagal reaction with syncope in blood donors at high risk for post-donation syncope. 86 The effect of water intake in these situations is thought to be due to effects on the sympathetic nervous system rather than to changes in blood volume. 83 , 84 Interestingly, in rare cases, individuals may experience bradycardia and syncope after swallowing cold liquids. 87 , – 89 While swallow syncope can be seen with substances other than water, swallow syncope further supports the notion that the result of water ingestion in the pressor effect has both a neural component as well as a cardiac component.

Water deprivation and dehydration can lead to the development of headache. 90 Although this observation is largely unexplored in the medical literature, some observational studies indicate that water deprivation, in addition to impairing concentration and increasing irritability, can serve as a trigger for migraine and can also prolong migraine. 91 , 92 In those with water deprivation-induced headache, ingestion of water provided relief from headache in most individuals within 30 min to 3 h. 92 It is proposed that water deprivation-induced headache is the result of intracranial dehydration and total plasma volume. Although provision of water may be useful in relieving dehydration-related headache, the utility of increasing water intake for the prevention of headache is less well documented.

The folk wisdom that drinking water can stave off headaches has been relatively unchallenged, and has more traction in the popular press than in the medical literature. Recently, one study examined increased water intake and headache symptoms in headache patients. 93 In this randomized trial, patients with a history of different types of headache, including migraine and tension headache, were either assigned to a placebo condition (a nondrug tablet) or the increased water condition. In the water condition, participants were instructed to consume an additional volume of 1.5 L water/day on top of what they already consumed in foods and fluids. Water intake did not affect the number of headache episodes, but it was modestly associated with reduction in headache intensity and reduced duration of headache. The data from this study suggest that the utility of water as prophylaxis is limited in headache sufferers, and the ability of water to reduce or prevent headache in the broader population remains unknown.

One of the more pervasive myths regarding water intake is its relation to improvements of the skin or complexion. By improvement, it is generally understood that individuals are seeking to have a more “moisturized” look to the surface skin, or to minimize acne or other skin conditions. Numerous lay sources such as beauty and health magazines as well as postings on the Internet suggest that drinking 8–10 glasses of water a day will “flush toxins from the skin” and “give a glowing complexion” despite a general lack of evidence 94 , 95 to support these proposals. The skin, however, is important for maintaining body water levels and preventing water loss into the environment.

The skin contains approximately 30% water, which contributes to plumpness, elasticity, and resiliency. The overlapping cellular structure of the stratum corneum and lipid content of the skin serves as “waterproofing” for the body. 96 Loss of water through sweat is not indiscriminate across the total surface of the skin, but is carried out by eccrine sweat glands, which are evenly distributed over most of the body surface. 97 Skin dryness is usually associated with exposure to dry air, prolonged contact with hot water and scrubbing with soap (both strip oils from the skin), medical conditions, and medications. While more serious levels of dehydration can be reflected in reduced skin turgor, 98 , 99 with tenting of the skin acting as a flag for dehydration, overt skin turgor in individuals with adequate hydration is not altered. Water intake, particularly in individuals with low initial water intake, can improve skin thickness and density as measured by sonogram, 100 offsets transepidermal water loss, and can improve skin hydration. 101 Adequate skin hydration, however, is not sufficient to prevent wrinkles or other signs of aging, which are related to genetics and to sun and environmental damage. Of more utility to individuals already consuming adequate fluids is the use of topical emollients; these will improve skin barrier function and improve the look and feel of dry skin. 102 , 103

Many chronic diseases have multifactorial origins. In particular, differences in lifestyle and the impact of environment are known to be involved and constitute risk factors that are still being evaluated. Water is quantitatively the most important nutrient. In the past, scientific interest with regard to water metabolism was mainly directed toward the extremes of severe dehydration and water intoxication. There is evidence, however, that mild dehydration may also account for some morbidities. 4 , 104 There is currently no consensus on a “gold standard” for hydration markers, particularly for mild dehydration. As a consequence, the effects of mild dehydration on the development of several disorders and diseases have not been well documented.

There is strong evidence showing that good hydration reduces the risk of urolithiasis (see Table 2 for evidence categories). Less strong evidence links good hydration with reduced incidence of constipation, exercise asthma, hypertonic dehydration in the infant, and hyperglycemia in diabetic ketoacidosis. Good hydration is associated with a reduction in urinary tract infections, hypertension, fatal coronary heart disease, venous thromboembolism, and cerebral infarct, but all these effects need to be confirmed by clinical trials. For other conditions such as bladder or colon cancer, evidence of a preventive effect of maintaining good hydration is not consistent (see Table 3 ).

Categories of evidence used in evaluating the quality of reports.

Data adapted from Manz. 104

Summary of evidence for association of hydration status with chronic diseases.

Categories of evidence: described in Table 2 .

Water consumption, water requirements, and energy intake are linked in fairly complex ways. This is partially because physical activity and energy expenditures affect the need for water but also because a large shift in beverage consumption over the past century or more has led to consumption of a significant proportion of our energy intake from caloric beverages. Nonregulatory beverage intake, as noted earlier, has assumed a much greater role for individuals. 19 This section reviews current patterns of water intake and then refers to a full meta-analysis of the effects of added water on energy intake. This includes adding water to the diet and water replacement for a range of caloric and diet beverages, including sugar-sweetened beverages, juice, milk, and diet beverages. The third component is a discussion of water requirements and suggestions for considering the use of mL water/kcal energy intake as a metric.

Patterns and trends of water consumption

Measurement of total fluid water consumption in free-living individuals is fairly new in focus. As a result, the state of the science is poorly developed, data are most likely fairly incomplete, and adequate validation of the measurement techniques used is not available. Presented here are varying patterns and trends of water intake for the United States over the past three decades followed by a brief review of the work on water intake in Europe.

There is really no existing information to support an assumption that consumption of water alone or beverages containing water affects hydration differentially. 3 , 105 Some epidemiological data suggest water might have different metabolic effects when consumed alone rather than as a component of caffeinated or flavored or sweetened beverages; however, these data are at best suggestive of an issue deserving further exploration. 106 , 107 As shown below, the research of Ershow et al. indicates that beverages not consisting solely of water do contain less than 100% water.

One study in the United States has attempted to examine all the dietary sources of water. 16 , 17 These data are cited in Table 4 as the Ershow study and were based on National Food Consumption Survey food and fluid intake data from 1977–1978. These data are presented in Table 4 for children aged 2–18 years (Panel A) and for adults aged 19 years and older (Panel B). Ershow et al. 16 , 17 spent a great deal of time working out ways to convert USDA dietary data into water intake, including water absorbed during the cooking process, water in food, and all sources of drinking water.

Beverage pattern trends in the United States for children aged 2–18 years and adults aged 19 years and older, (nationally representative).

Note: The data are age and sex adjusted to 1965.

Values stem from the Ershow calculations. 16

These researchers created a number of categories and used a range of factors measured in other studies to estimate the water categories. The water that is found in food, based on food composition table data, was 393 mL for children. The water that was added as a result of cooking (e.g., rice) was 95 mL. Water consumed as a beverage directly as water was 624 mL. The water found in other fluids, as noted, comprised the remainder of the milliliters, with the highest levels in whole-fat milk and juices (506 mL). There is a small discrepancy between the Ershow data regarding total fluid intake measures for these children and the normal USDA figures. That is because the USDA does not remove milk fats and solids, fiber, and other food constituents found in beverages, particularly juice and milk.

A key point illustrated by these nationally representative US data is the enormous variability between survey waves in the amount of water consumed (see Figure 1 , which highlights the large variation in water intake as measured in these surveys). Although water intake by adults and children increased and decreased at the same time, for reasons that cannot be explained, the variation was greater among children than adults. This is partly because the questions the surveys posed varied over time and there was no detailed probing for water intake, because the focus was on obtaining measures of macro- and micronutrients. Dietary survey methods used in the past have focused on obtaining data on foods and beverages containing nutrient and non-nutritive sweeteners but not on water. Related to this are the huge differences between the the USDA surveys and the National Health and Nutrition Examination Survey (NHANES) performed in 1988–1994 and in 1999 and later. In addition, even the NHANES 1999–2002 and 2003–2006 surveys differ greatly. These differences reflect a shift in the mode of questioning with questions on water intake being included as part of a standard 24-h recall rather than as stand-alone questions. Water intake was not even measured in 1965, and a review of the questionnaires and the data reveals clear differences in the way the questions have been asked and the limitations on probes regarding water intake. Essentially, in the past people were asked how much water they consumed in a day and now they are asked for this information as part of a 24-h recall survey. However, unlike for other caloric and diet beverages, there are limited probes for water alone. The results must thus be viewed as crude approximations of total water intake without any strong research to show if they are over- or underestimated. From several studies of water and two ongoing randomized controlled trials performed by us, it is clear that probes that include consideration of all beverages and include water as a separate item result in the provision of more complete data.

Water consumption trends from USDA and NHANES surveys (mL/day/capita), nationally representative. Note: this includes water from fluids only, excluding water in foods. Sources for 1965, 1977–1978, 1989–1991, and 1994–1998, are USDA. Others are NHANES and 2005–2006 is joint USDA and NHANES.

Water consumption data for Europe are collected far more selectively than even the crude water intake questions from NHANES. A recent report from the European Food Safety Agency provides measures of water consumption from a range of studies in Europe. 4 , – 109 Essentially, what these studies show is that total water intake is lower across Europe than in the United States. As with the US data, none are based on long-term, carefully measured or even repeated 24-h recall measures of water intake from food and beverages. In an unpublished examination of water intake in UK adults in 1986–1987 and in 2001–2002, Popkin and Jebb have found that although intake increased by 226 mL/day over this time period, it was still only 1,787 mL/day in the latter period (unpublished data available from BP); this level is far below the 2,793 mL/day recorded in the United States for 2005–2006 or the earlier US figures for comparably aged adults.

A few studies have been performed in the United States and Europe utilizing 24-h urine and serum osmolality measures to determine total water turnover and hydration status. Results of these studies suggest that US adults consume over 2,100 mL of water per day while adults in Europe consume less than half a liter. 4 , 110 Data on total urine collection would appear to be another useful measure for examining total water intake. Of course, few studies aside from the Donald Study of an adolescent cohort in Germany have collected such data on population levels for large samples. 109

Effects of water consumption on overall energy intake

There is an extensive body of literature that focuses on the impact of sugar-sweetened beverages on weight and the risk of obesity, diabetes, and heart disease; however, the perspective of providing more water and its impact on health has not been examined. The literature on water does not address portion sizes; instead, it focuses mainly on water ad libitum or in selected portions compared with other caloric beverages. A detailed meta-analysis of the effects of water intake alone (i.e., adding additional water) and as a replacement for sugar-sweetened beverages, juice, milk, and diet beverages appears elsewhere. 111

In general, the results of this review suggest that water, when consumed in place of sugar-sweetened beverages, juice, and milk, is linked with reduced energy intake. This finding is mainly derived from clinical feeding studies but also from one very good randomized, controlled school intervention and several other epidemiological and intervention studies. Aside from the issue of portion size, factors such as the timing of beverage and meal intake (i.e., the delay between consumption of the beverage and consumption of the meal) and types of caloric sweeteners remain to be considered. However, when beverages are consumed in normal free-living conditions in which five to eight daily eating occasions are the norm, the delay between beverage and meal consumption may matter less. 112 , – 114

The literature on the water intake of children is extremely limited. However, the excellent German school intervention with water suggests the effects of water on the overall energy intake of children might be comparable to that of adults. 115 In this German study, children were educated on the value of water and provided with special filtered drinking fountains and water bottles in school. The intervention schoolchildren increased their water intake by 1.1 glasses/day ( P  < 0.001) and reduced their risk of overweight by 31% (OR = 0.69, P  = 0.40).

Classically, water data are examined in terms of milliliters (or some other measure of water volume consumed per capita per day by age group). This measure does not link fluid intake and caloric intake. Disassociation of fluid and calorie intake is difficult for clinicians dealing with older persons with reduced caloric intake. This milliliter water measure assumes some mean body size (or surface area) and a mean level of physical activity – both of which are determinants of not only energy expenditure but also water balance. Children are dependent on adults for access to water, and studies suggest that their larger surface area to volume ratio makes them susceptible to changes in skin temperatures linked with ambient temperature shifts. 116 One option utilized by some scholars is to explore food and beverage intake in milliliters per kilocalorie (mL/kcal), as was done in the 1989 US recommended dietary allowances. 4 , 117 This is an option that is interpretable for clinicians and which incorporates, in some sense, body size or surface area and activity. Its disadvantage is that water consumed with caloric beverages affects both the numerator and the denominator; however, an alternative measure that could be independent of this direct effect on body weight and/or total caloric intake is not presently known.

Despite its critical importance in health and nutrition, the array of available research that serves as a basis for determining requirements for water or fluid intake, or even rational recommendations for populations, is limited in comparison with most other nutrients. While this deficit may be partly explained by the highly sensitive set of neurophysiological adaptations and adjustments that occur over a large range of fluid intakes to protect body hydration and osmolarity, this deficit remains a challenge for the nutrition and public health community. The latest official effort at recommending water intake for different subpopulations occurred as part of the efforts to establish Dietary Reference Intakes in 2005, as reported by the Institute of Medicine of the National Academies of Science. 3 As a graphic acknowledgment of the limited database upon which to express estimated average requirements for water for different population groups, the Committee and the Institute of Medicine stated: “While it might appear useful to estimate an average requirement (an EAR) for water, an EAR based on data is not possible.” Given the extreme variability in water needs that are not solely based on differences in metabolism, but also on environmental conditions and activities, there is not a single level of water intake that would assure adequate hydration and optimum health for half of all apparently healthy persons in all environmental conditions. Thus, an adequate intake (AI) level was established in place of an EAR for water.

The AIs for different population groups were set as the median water intakes for populations, as reported in the National Health and Nutrition Examination Surveys; however, the intake levels reported in these surveys varied greatly based on the survey years (e.g., NHANES 1988–1994 versus NHANES 1999–2002) and were also much higher than those found in the USDA surveys (e.g., 1989–1991, 1994–1998, or 2005–2006). If the AI for adults, as expressed in Table 5 , is taken as a recommended intake, the wisdom of converting an AI into a recommended water or fluid intake seems questionable. The first problem is the almost certain inaccuracy of the fluid intake information from the national surveys, even though that problem may also exist for other nutrients. More importantly, from the standpoint of translating an AI into a recommended fluid intake for individuals or populations, is the decision that was made when setting the AI to add an additional roughly 20% of water intake, which is derived from some foods in addition to water and beverages. While this may have been a legitimate effort to use total water intake as a basis for setting the AI, the recommendations that derive from the IOM report would be better directed at recommendations for water and other fluid intake on the assumption that the water content of foods would be a “passive” addition to total water intake. In this case, the observations of the dietary reference intake committee that it is necessary for water intake to meet needs imposed by metabolism and environmental conditions must be extended to consider three added factors, namely body size, gender, and physical activity. Those are the well-studied factors that allow a rather precise measurement and determination of energy intake requirements. It is, therefore, logical that those same factors might underlie recommendations to meet water intake needs in the same populations and individuals. Consideration should also be given to the possibility that water intake needs would best be expressed relative to the calorie requirements, as is done regularly in the clinical setting, and data should be gathered to this end through experimental and population research.

Water requirements expressed in relation to energy recommendations.

AI for total fluids derived from dietary reference intakes for water, potassium, sodium, chloride, and sulphate.

Ratios for water intake based on the AI for water in liters/day calculated using EER for each range of physical activity. EER adapted from the Institute of Medicine Dietary Reference Intakes Macronutrients Report, 2002.

It is important to note that only a few countries include water on their list of nutrients. 118 The European Food Safety Authority is developing a standard for all of Europe. 105 At present, only the United States and Germany provide AI values for water. 3 , 119

Another approach to the estimation of water requirements, beyond the limited usefulness of the AI or estimated mean intake, is to express water intake requirements in relation to energy requirements in mL/kcal. An argument for this approach includes the observation that energy requirements for each age and gender group are strongly evidence-based and supported by extensive research taking into account both body size and activity level, which are crucial determinants of energy expenditure that must be met by dietary energy intake. Such measures of expenditure have used highly accurate methods, such as doubly labeled water; thus, estimated energy requirements have been set based on solid data rather than the compromise inherent in the AIs for water. Those same determinants of energy expenditure and recommended intake are also applicable to water utilization and balance, and this provides an argument for pegging water/fluid intake recommendations to the better-studied energy recommendations. The extent to which water intake and requirements are determined by energy intake and expenditure is understudied, but in the clinical setting it has long been practice to supply 1 mL/kcal administered by tube to patients who are unable to take in food or fluids. Factors such as fever or other drivers of increased metabolism affect both energy expenditure and fluid loss and are thus linked in clinical practice. This concept may well deserve consideration in the setting of population intake goals.

Finally, for decades there has been discussion about expressing nutrient requirements per 1,000 kcal so that a single number would apply reasonably across the spectrum of age groups. This idea, which has never been adopted by the Institute of Medicine and the National Academies of Science, may lend itself to an improved expression of water/fluid intake requirements, which must eventually replace the AIs. Table 5 presents the IOM water requirements and then develops a ratio of mL/kcal based on them. The European Food Safety Agency refers positively to the possibility of expressing water intake recommendations in mL/kcal as a function of energy requirements. 105 Outliers in the adult male categories, which reach ratios as high as 1.5, may well be based on the AI data from the United States, which are above those in the more moderate and likely more accurate European recommendations.

The topic of utilizing mL/kcal to examine water intake and water gaps is explored in Table 6 , which takes the full set of water intake AIs for each age-gender grouping and examines total intake. The data suggest a high level of fluid deficiency. Since a large proportion of fluids in the United States is based on caloric beverages and this proportion has changed markedly over the past 30 years, fluid intake increases both the numerator and the denominator of this mL/kcal relationship. Nevertheless, even using 1 mL/kcal as the AI would leave a gap for all children and adolescents. The NHANES physical activity data were also translated into METS/day to categorize all individuals by physical activity level and thus varying caloric requirements. Use of these measures reveals a fairly large fluid gap, particularly for adult males as well as children ( Table 6 ).

Water intake and water intake gaps based on US Water Adequate Intake Recommendations (based on utilization of water and physical activity data from NHANES 2005–2006).

Note: Recommended water intake for actual activity level is the upper end of the range for moderate and active.

A weighted average for the proportion of individuals in each METS-based activity level.

This review has pointed out a number of issues related to water, hydration, and health. Since water is undoubtedly the most important nutrient and the only one for which an absence will prove lethal within days, understanding of water measurement and water requirements is very important. The effects of water on daily performance and short- and long-term health are quite clear. The existing literature indicates there are few negative effects of water intake while the evidence for positive effects is quite clear.

Little work has been done to measure total fluid intake systematically, and there is no understanding of measurement error and best methods of understanding fluid intake. The most definitive US and European documents on total water requirements are based on these extant intake data. 3 , 105 The absence of validation methods for water consumption intake levels and patterns represents a major gap in knowledge. Even varying the methods of probing in order to collect better water recall data has been little explored.

On the other side of the issue is the need to understand total hydration status. There are presently no acceptable biomarkers of hydration status at the population level, and controversy exists about the current knowledge of hydration status among older Americans. 6 , 120 Thus, while scholars are certainly focused on attempting to create biomarkers for measuring hydration status at the population level, the topic is currently understudied.

As noted, the importance of understanding the role of fluid intake on health has emerged as a topic of increasing interest, partially because of the trend toward rising proportions of fluids being consumed in the form of caloric beverages. The clinical, epidemiological, and intervention literature on the effects of added water on health are covered in a related systematic review. 111 The use of water as a replacement for sugar-sweetened beverages, juice, or whole milk has clear effects in that energy intake is reduced by about 10–13% of total energy intake. However, only a few longer-term systematic interventions have investigated this topic and no randomized, controlled, longer-term trials have been published to date. There is thus very minimal evidence on the effects of just adding water to the diet and of replacing water with diet beverages.

There are many limitations to this review. One certainly is the lack of discussion of potential differences in the metabolic functioning of different types of beverages. 121 Since the literature in this area is sparse, however, there is little basis for delving into it at this point. A discussion of the potential effects of fructose (from all caloric sweeteners when consumed in caloric beverages) on abdominal fat and all of the metabolic conditions directly linked with it (e.g., diabetes) is likewise lacking. 122 , – 125 A further limitation is the lack of detailed review of the array of biomarkers being considered to measure hydration status. Since there is no measurement in the field today that covers more than a very short time period, except for 24-hour total urine collection, such a discussion seems premature.

Some ways to examine water requirements have been suggested in this review as a means to encourage more dialogue on this important topic. Given the significance of water to our health and of caloric beverages to our total energy intake, as well as the potential risks of nutrition-related noncommunicable diseases, understanding both the requirements for water in relation to energy requirements, and the differential effects of water versus other caloric beverages, remain important outstanding issues.

This review has attempted to provide some sense of the importance of water to our health, its role in relationship to the rapidly increasing rates of obesity and other related diseases, and the gaps in present understanding of hydration measurement and requirements. Water is essential to our survival. By highlighting its critical role, it is hoped that the focus on water in human health will sharpen.

The authors wish to thank Ms. Frances L. Dancy for administrative assistance, Mr. Tom Swasey for graphics support, Dr. Melissa Daniels for assistance, and Florence Constant (Nestle's Water Research) for advice and references.

This work was supported by the Nestlé Waters, Issy-les-Moulineaux, France, 5ROI AGI0436 from the National Institute on Aging Physical Frailty Program, and NIH R01-CA109831 and R01-CA121152.

Declaration of interest

The authors have no relevant interests to declare.

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Why You Can Hear the Temperature of Water

A science video maker in China couldn’t find a good explanation for why hot and cold water sound different, so he did his own research and published it.

By Sam Kean

Most people are quite good at distinguishing between the sound of a hot liquid and the sound of a cold one being poured, even if they don’t realize it.

“Every time I give a talk and I say, ‘Surprisingly, adults can tell the difference between hot and cold water,’ people just go like this,” said Tanushree Agrawal, a psychologist who, during a video call, mimicked audience members shaking their heads no. But research she completed at the University of California at San Diego demonstrated that three-fourths of the participants in her experiments could in fact detect the difference.

You can try it yourself. Put on your headphones or listen closely to your computer or phone’s speaker and hit play on this audio recording.

Can You Hear the Temperature?

Could you tell which sound was hot and which was cold?

If you said the first one was cold, congratulations: You’re in Dr. Agrawal’s majority.

In general, cold water sounds brighter and splashier, while hot water sounds duller and frothier. But until recently no one really had evidence to explain the difference.

However, Xiaotian Bi, who earned a Ph.D. in chemical engineering last year from Tsinghua University in Beijing, offers a new explanation in a paper he and colleagues published in March on the arXiv website. It’s all about the size of the bubbles that form during pouring, he says, and this insight may have implications for how we enjoy everyday food and drink.

Dr. Bi’s paper has not yet been through peer review, and he acknowledges that much more research is needed. But Joshua Reiss, a professor of audio engineering at Queen Mary University of London, who has also studied the acoustics of hot and cold water, said he was “on the right track, for sure.”

Discussions of the varying sounds of hot and cold liquids usually point to differences in viscosity as the culprit. But Dr. Bi wasn’t satisfied with that reasoning. He produces and stars in his own popular science videos , and decided that the sounds water makes at different temperatures was a good topic . He poked around looking for published research on the subject and came away disappointed.

“None of them gave a precise explanation,” he said, adding that it was “an unsolved mystery.”

So Dr. Bi decided to do his own scientific investigation, which would inform his video. He used his expertise in fluid dynamics to explore the role played by bubbles, which actually create most of the sound we hear in moving water. You can observe this in waves, which glide along silently until they break, at which point they fall and trap air that produces noise as the bubbles resonate briefly within the water.

Previous research showed that larger air bubbles in liquids produce lower-frequency sounds. Dr. Bi also found that the acoustical spectrum of hot water has more low-frequency sounds than the spectrum of cold water. He wondered, then, whether pouring hot water into a container would trap larger bubbles than pouring cold would, and whether that might explain the difference in sounds.

His hunch proved correct. Dr. Bi purchased a container with a spigot to dispense water in a controlled fashion, first at 50 degrees Fahrenheit, then at 194 degrees. High-resolution videos and photographs revealed that hot water consistently produced bubbles 5 to 10 millimeters in size, while cold water produced bubbles around 1 to 2 millimeters.

(That’s why the cold water is on the left side of your screen in video above, and the hot water on the right)

In addition to offering an explanation of something that people hear, the research also provides insight into how we enjoy food and drink in general. Consider coffee.

Coffee tastes delicious when hot, but gunky and bitter when cold. That’s because aromatic flavor molecules jump off the surface of hot beverages more readily. And that link between flavor and temperature can produce a Pavlovian response in coffee drinkers.

This is consistent with an observation by Charles Spence, a psychologist who heads the Crossmodal Research Laboratory at Oxford and has won an Ig-Nobel Prize for research on the links between sound and taste when potato chips are consumed. In a 2021 paper, he wrote that “the sound of temperature likely helps to subtly set people’s aromatic flavor expectations,” even if unconsciously.

“Very often we taste what we predict,” he said. It’s all part of what he calls the hidden “sonic seasoning” of food and drinks.

Suggestions or feedback?

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Two MIT PhD students awarded J-WAFS fellowships for their research on water

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Since 2014, the Abdul Latif Jameel Water and Food Systems Lab (J-WAFS) has advanced interdisciplinary research aimed at solving the world's most pressing water and food security challenges to meet human needs. In 2017, J-WAFS established the Rasikbhai L. Meswani Water Solutions Fellowship and the J-WAFS Graduate Student Fellowship. These fellowships provide support to outstanding MIT graduate students who are pursuing research that has the potential to improve water and food systems around the world. 

Recently, J-WAFS awarded the 2024-25 fellowships to Jonathan Bessette and Akash Ball, two MIT PhD students dedicated to addressing water scarcity by enhancing desalination and purification processes. This work is of important relevance since the world's freshwater supply has been steadily depleting due to the effects of climate change. In fact, one-third of the global population lacks access to safe drinking water. Bessette and Ball are focused on designing innovative solutions to enhance the resilience and sustainability of global water systems. To support their endeavors, J-WAFS will provide each recipient with funding for one academic semester for continued research and related activities.

“This year, we received many strong fellowship applications,” says J-WAFS executive director Renee J. Robins. “Bessette and Ball both stood out, even in a very competitive pool of candidates. The award of the J-WAFS fellowships to these two students underscores our confidence in their potential to bring transformative solutions to global water challenges.”

2024-25 Rasikbhai L. Meswani Fellowship for Water Solutions

The Rasikbhai L. Meswani Fellowship for Water Solutions is a doctoral fellowship for students pursuing research related to water and water supply at MIT. The fellowship is made possible by Elina and Nikhil Meswani and family. 

Jonathan Bessette is a doctoral student in the Global Engineering and Research (GEAR) Center within the Department of Mechanical Engineering at MIT, advised by Professor Amos Winter. His research is focused on water treatment systems for the developing world, mainly desalination, or the process in which salts are removed from water. Currently, Bessette is working on designing and constructing a low-cost, deployable, community-scale desalination system for humanitarian crises.

In arid and semi-arid regions, groundwater often serves as the sole water source, despite its common salinity issues. Many remote and developing areas lack reliable centralized power and water systems, making brackish groundwater desalination a vital, sustainable solution for global water scarcity. 

“An overlooked need for desalination is inland groundwater aquifers, rather than in coastal areas,” says Bessette. “This is because much of the population lives far enough from a coast that seawater desalination could never reach them. My work involves designing low-cost, sustainable, renewable-powered desalination technologies for highly constrained situations, such as drinking water for remote communities,” he adds.

To achieve this goal, Bessette developed a batteryless, renewable electrodialysis desalination system. The technology is energy-efficient, conserves water, and is particularly suited for challenging environments, as it is decentralized and sustainable. The system offers significant advantages over the conventional reverse osmosis method, especially in terms of reduced energy consumption for treating brackish water. Highlighting Bessette’s capacity for engineering insight, his advisor noted the “simple and elegant solution” that Bessette and a staff engineer, Shane Pratt, devised that negated the need for the system to have large batteries. Bessette is now focusing on simplifying the system’s architecture to make it more reliable and cost-effective for deployment in remote areas.

Growing up in upstate New York, Bessette completed a bachelor's degree at the State University of New York at Buffalo. As an undergrad, he taught middle and high school students in low-income areas of Buffalo about engineering and sustainability. However, he cited his junior-year travel to India and his experience there measuring water contaminants in rural sites as cementing his dedication to a career addressing food, water, and sanitation challenges. In addition to his doctoral research, his commitment to these goals is further evidenced by another project he is pursuing, funded by a J-WAFS India grant, that uses low-cost, remote sensors to better understand water fetching practices. Bessette is conducting this work with fellow MIT student Gokul Sampath in order to help families in rural India gain access to safe drinking water.

2024-25 J-WAFS Graduate Student Fellowship for Water and Food Solutions

The J-WAFS Graduate Student Fellowship is supported by the J-WAFS Research Affiliate Program , which offers companies the opportunity to engage with MIT on water and food research. Current fellowship support was provided by two J-WAFS Research Affiliates: Xylem , a leading U.S.-based provider of water treatment and infrastructure solutions, and GoAigua , a Spanish company at the forefront of digital transformation in the water industry through innovative solutions. 

Akash Ball is a doctoral candidate in the Department of Chemical Engineering, advised by Professor Heather Kulik. His research focuses on the computational discovery of novel functional materials for energy-efficient ion separation membranes with high selectivity. Advanced membranes like these are increasingly needed for applications such as water desalination, battery recycling, and removal of heavy metals from industrial wastewater. 

“Climate change, water pollution, and scarce freshwater reserves cause severe water distress for about 4 billion people annually, with 2 billion in India and China’s semiarid regions,” Ball notes. “One potential solution to this global water predicament is the desalination of seawater, since seawater accounts for 97 percent of all water on Earth.”

Although several commercial reverse osmosis membranes are currently available, these membranes suffer several problems, like slow water permeation, permeability-selectivity trade-off, and high fabrication costs. Metal-organic frameworks (MOFs) are porous crystalline materials that are promising candidates for highly selective ion separation with fast water transport due to high surface area, the presence of different pore windows, and the tunability of chemical functionality. In the Kulik lab, Ball is developing a systematic understanding of how MOF chemistry and pore geometry affect water transport and ion rejection rates. By the end of his PhD, Ball plans to identify existing, best-performing MOFs with unparalleled water uptake using machine learning models, propose novel hypothetical MOFs tailored to specific ion separations from water, and discover experimental design rules that enable the synthesis of next-generation membranes.  

Ball’s advisor praised the creativity he brings to his research, and his leadership skills that benefit her whole lab. Before coming to MIT, Ball obtained a master’s degree in chemical engineering from the Indian Institute of Technology (IIT) Bombay and a bachelor’s degree in chemical engineering from Jadavpur University in India. During a research internship at IIT Bombay in 2018, he worked on developing a technology for in situ arsenic detection in water. Like Bessette, he noted the impact of this prior research experience on his interest in global water challenges, along with his personal experience growing up in an area in India where access to safe drinking water was not guaranteed.

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• Kulik Research Group
• Abdul Latif Jameel Water and Food Systems Lab (J-WAFS)
• K. Lisa Yang Global Engineering and Research (GEAR) Center
• Department of Chemical Engineering
• Department of Mechanical Engineering

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• Chemical engineering
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Water Research Hub Earns 5 More Years of Funding

The national alliance for water innovation will continue work to make us water supplies more accessible, affordable, and energy efficient.

Most Americans get their water from traditional sources, like large freshwater reservoirs or groundwater—fresh, underground rivers flowing beneath our feet.

But change is coming.

Climate change, population growth, and increased industrial and agricultural production are several factors (among many) that are stressing U.S. and global freshwater supplies.

“To supply the water needs of the future, it is critical that the United States develop technologies that provide alternative water sources,” said Abhishek Roy, a senior staff scientist at the National Renewable Energy Laboratory (NREL) and member of the National Alliance for Water Innovation (NAWI).

And NAWI is doing exactly that.

A National Hub Earns More Support

First launched in 2019, NAWI is a research hub that brings together a world-class team of partners from industry and academia, as well as the hub’s public membership organization, called the NAWI Alliance . Together, these experts and water treatment stakeholders are working to lower the cost and energy of water purification technologies, including those that can transform nontraditional water sources, like wastewater or salty groundwater, into clean drinking water.

As of April 2024, NAWI has been extended for five more years, so the team can continue to hone water treatment technologies and increase access to clean drinking water for all Americans, all while reducing the energy and emissions associated with water treatment processes. The organization has received $75 million in funding from two U.S. Department of Energy (DOE) offices: the Industrial Efficiency and Decarbonization Office and the Water Power Technologies Office.

“The extension is great news,” said Matthew Ringer, the laboratory program manager for advanced manufacturing at NREL and NAWI’s partnerships director. “NAWI has more than 460 organizations and more than 1,800 members from around the world who are working together to help produce secure, reliable, and affordable water for communities that are most in need.”

NAWI is led by DOE’s Lawrence Berkeley National Laboratory in partnership with NREL, Oak Ridge National Laboratory, and the National Energy Technology Laboratory.

A Master Road Map to More Secure, Affordable Water

In its first five years, NAWI accomplished a lot—with help from its many members, including researchers at NREL. NREL’s Jordan Macknick led an early NAWI win: a master road map that identifies the highest-priority research needs for water desalination (or purification) and where such technologies are already in use. From the beginning, this road map helped NAWI members optimize their investments; it also serves as the foundation—and future guide—for NAWI’s five-year extension. Macknick also leads one of NAWI’s core research areas—the Data Modeling and Analysis topic area —which focuses on analyzing the cost, efficiency, and performance of entire water treatment systems.

This type of research also happens to be one of NREL’s areas of expertise.

For example, NREL’s Kurban Sitterley helped improve an open-source software tool that can assess the technological and economic value of more than 60 different water treatment technologies. Water treatment researchers and facilities can use the tool, called the Water Treatment Technoeconomic Assessment Platform (or WaterTAP), to evaluate technologies that could help reduce their costs and energy consumption while continuing to meet existing and future water demands. (Sitterley also developed a new model for WaterTAP that can evaluate one of the most promising ways to remove forever chemicals and other contaminants from drinking water).

Plus, WaterTAP can help assess how water treatment facilities could use renewable energy resources, like solar, wind, and geothermal, along with batteries to power their facilities without raising their costs. Some community-scale treatment systems could even provide water for disaster relief and recovery missions or remote military deployments.

“This funding extension is essential to continue the maturation of these technologies and improve their cost and performance,” said Scott Struck, a senior integrated water systems research scientist at NREL.

Solutions for Communities With Dwindling or Contaminated Water Supplies

Struck appreciates how much NAWI has advanced water treatment tools, technologies, policies, and planning. But he is especially excited about NAWI’s work with communities. Even in the United States, not all communities have access to uncontaminated drinking water. In one area of the Central Valley of California, the available drinking water contains high levels of arsenic (a carcinogen), making it unsafe to drink. Because the community is small and financially unable to shoulder the costs of a centralized water treatment system, the residents resorted to buying bottled water instead.

But with NAWI’s help, the community could receive a more affordable and sustainable solution: smaller, more modular water treatment technologies that can filter out enough arsenic to achieve drinking water standards. With that, the community could access a local, more affordable water supply.

In NAWI’s next five years—which has been dubbed NAWI 2.0—the organization will pursue more community-based projects to help Americans maintain affordable and effective drinking water even as hotter temperatures or droughts threaten their supplies. NAWI Alliance members will also continue to advance desalination and other novel technologies that can treat unconventional water sources and cut greenhouse gas emissions at the same time.

“NREL is excited that DOE has extended NAWI for another five years,” Ringer said. “We look forward to working with our partners in national labs, academia, and industry to drive solutions for decarbonizing water and wastewater sectors.”

“Working together,” Struck added, “the NAWI community will help secure a more sustainable and resilient water supply.”

Become a thought leader in clean water innovation and join the NAWI Alliance for free today to unite with world-class lab, industry, and academic experts to address some of the greatest water and energy security challenges.

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Venus has almost no water. A new study may reveal why

Illustration of what Venus may have looked like billions of years ago with water, left, and what Venus looks like today, right. (Credits: NASA; NASA/JPL-Caltech)  

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Planetary scientists at CU Boulder have discovered how Venus, Earth’s scalding and uninhabitable neighbor, became so dry.

The new study fills in a big gap in what the researchers call “the water story on Venus.” Using computer simulations, the team found that hydrogen atoms in the planet’s atmosphere go whizzing into space through a process known as “dissociative recombination”—causing Venus to lose roughly twice as much water every day compared to previous estimates.

In Venus' upper atmosphere, hydrogen atoms, orange, whiz into space, leaving behind carbon monoxide molecules, blue and purple. (Credit: Aurore Simonnet/LASP/CU Boulder)

The team  published their findings May 6 in the journal Nature. The results could help to explain what happens to water in a host of planets across the galaxy.

“Water is really important for life,” said Eryn Cangi, a research scientist at the Laboratory for Atmospheric and Space Physics (LASP) and co-lead author of the new paper. “We need to understand the conditions that support liquid water in the universe, and that may have produced the very dry state of Venus today.”

Venus, she added, is positively parched. If you took all the water on Earth and spread it over the planet like jam on toast, you’d get a liquid layer roughly 3 kilometers (1.9 miles) deep. If you did the same thing on Venus, where all the water is trapped in the air, you’d wind up with only 3 centimeters (1.2 inches), barely enough to get your toes wet.

“Venus has 100,000 times less water than the Earth, even though it’s basically the same size and mass,” said Michael Chaffin, co-lead author of the study and a research scientist at LASP.

In the current study, the researchers used computer models to understand Venus as a gigantic chemistry laboratory, zooming in on the diverse reactions that occur in the planet’s swirling atmosphere. The group reports that a molecule called HCO+ (an ion made up of one atom each of hydrogen, carbon and oxygen) high in Venus’ atmosphere may be the culprit behind the planet’s escaping water. 

For Cangi, co-lead author of the research, the findings reveal new hints about why Venus, which probably once looked almost identical to Earth, is all but unrecognizable today.

“We’re trying to figure out what little changes occurred on each planet to drive them into these vastly different states,” said Cangi, who earned her doctorate in astrophysical and planetary sciences at CU Boulder in 2023.

Spilling the water

Venus, she noted, wasn’t always such a desert.

Scientists suspect that billions of year ago during the formation of Venus, the planet received about as much water as Earth. At some point, catastrophe struck. Clouds of carbon dioxide in Venus’ atmosphere kicked off the most powerful greenhouse effect in the solar system, eventually raising temperatures at the surface to a roasting 900 degrees Fahrenheit. In the process, all of Venus’ water evaporated into steam, and most drifted away into space.

But that ancient evaporation can’t explain why Venus is as dry as it is today, or how it continues to lose water to space.

“As an analogy, say I dumped out the water in my water bottle. There would still be a few droplets left,” Chaffin said.

On Venus, however, almost all of those remaining drops also disappeared. The culprit, according to the new work, is elusive HCO+.

Missions to Venus

Chaffin and Cangi explained that in planetary upper atmospheres, water mixes with carbon dioxide to form this molecule. In previous research, the researchers reported that HCO+ may be responsible for Mars losing a big chunk of its water.

Illustration of NASA's DAVINCI probe falling to the surface of Venus. (Credit: NASA GSFC visualization by CI Labs Michael Lentz and others)

Here’s how it works on Venus: HCO+ is produced constantly in the atmosphere, but individual ions don’t survive for long. Electrons in the atmosphere find these ions, and recombine to split the ions in two. In the process, hydrogen atoms zip away and may even escape into space entirely—robbing Venus of one of the two components of water.

In the new study, the group calculated that the only way to explain Venus’ dry state was if the planet hosted larger than expected volumes of HCO+ in its atmosphere. There is one twist to the team’s findings. Scientists have never observed HCO+ around Venus. Chaffin and Cangi suggest that’s because they’ve never had the instruments to properly look.

While dozens of missions have visited Mars in recent decades, far fewer spacecraft have traveled to the second planet from the sun. None have carried instruments capable of detecting the HCO+ that powers the team’s newly discovered escape route.

“One of the surprising conclusions of this work is that HCO+ should actually be among the most abundant ions in the Venus atmosphere,” Chaffin said.

In recent years, however, a growing number of scientists have set their sights on Venus. NASA’s planned Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging (DAVINCI) mission, for example, will drop a probe through the planet’s atmosphere all the way to the surface. It’s scheduled to launch by the end of the decade.

DAVINCI won’t be able to detect HCO+, either, but the researchers are hopeful that a future mission might—revealing another key piece of the story of water on Venus.

“There haven’t been many missions to Venus,” Cangi said. “But newly planned missions will leverage decades of collective experience and a flourishing interest in Venus to explore the extremes of planetary atmospheres, evolution and habitability.”

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• Open access
• Published: 22 July 2020

Hydrogen-rich water reduces inflammatory responses and prevents apoptosis of peripheral blood cells in healthy adults: a randomized, double-blind, controlled trial

• Minju Sim 1 ,
• Chong-Su Kim 1 ,
• Woo-Jeong Shon 1 ,
• Young-Kwan Lee 2 ,
• Eun Young Choi 2 &
• Dong-Mi Shin 1 , 3  

Scientific Reports volume  10 , Article number:  12130 ( 2020 ) Cite this article

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• Cell biology
• Molecular biology

The evidence for the beneficial effects of drinking hydrogen-water (HW) is rare. We aimed to investigate the effects of HW consumption on oxidative stress and immune functions in healthy adults using systemic approaches of biochemical, cellular, and molecular nutrition. In a randomized, double-blind, placebo-controlled study, healthy adults (20–59 y) consumed either 1.5 L/d of HW ( n  = 20) or plain water (PW, n  = 18) for 4 weeks. The changes from baseline to the 4th week in serum biological antioxidant potential (BAP), derivatives of reactive oxygen, and 8-Oxo-2′-deoxyguanosine did not differ between groups; however, in those aged ≥ 30 y, BAP increased greater in the HW group than the PW group. Apoptosis of peripheral blood mononuclear cells (PBMCs) was significantly less in the HW group. Flow cytometry analysis of CD4 + , CD8 + , CD20 + , CD14 + and CD11b + cells showed that the frequency of CD14 + cells decreased in the HW group. RNA-sequencing analysis of PBMCs demonstrated that the transcriptomes of the HW group were clearly distinguished from those of the PW group. Most notably, transcriptional networks of inflammatory responses and NF-κB signaling were significantly down-regulated in the HW group. These finding suggest HW increases antioxidant capacity thereby reducing inflammatory responses in healthy adults.

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Introduction.

Oxidative stress indicates a state where excessive reactive oxygen species (ROS) overwhelm the biological antioxidant capacity, leading to disruption of ROS homeostasis and cellular damage 1 . It is important for cells to maintain moderate levels of ROS to perform normal physiological functions 2 . Excessive level of ROS are responsible for oxidative damage of DNA and lipids, which may lead to cellular death 3 . Also, oxidative stress may provoke inflammatory responses 3 , 4 that can further enhance oxidative stress. As a result, oxidative stress can act to precipitate chronic inflammation, with pathological conditions triggering various disorders including cardiovascular diseases, metabolic syndrome, neurodegenerative disorders, and cancer 5 , 6 , 7 , 8 .

There is no doubt that oxidative stress plays a central role in the pathogenesis of various chronic diseases. As a result, it has been of increasing interest to assess adjuvant effects of antioxidant agents in food on prevention and alleviation of these diseases. Recently, the US Food and Drug Administration acknowledged hydrogen (H 2 ) gas as food additives when used in drinking water or beverages and declared them to be generally recognized as safe. H 2 can be a novel antioxidant because of its ability to selectively scavenge strong oxidants such as hydroxyl radical 9 . In models of ischemia/reperfusion injury, H 2 prevented tissue damage and reduced infarct size 10 , 11 , 12 . In rat models of neurodegenerative disorders, including Parkinson’s and Alzheimer’s diseases, administration of H 2 improved the memory function of rats and retarded the progression of disease 13 , 14 . Some clinical trials have also determined the effect of H 2 on the several diseases including metabolic syndrome, rheumatoid arthritis, chronic hepatitis B and Parkinson’s disease 15 , 16 , 17 , 18 .

Despite the increasing evidence attesting to the beneficial effects of H 2 , to our knowledge, few studies have been conducted in a healthy population. Furthermore, the systemic effect of H 2 administration has not been elucidated because most of the preceding studies have only focused on measuring limited markers. Here, we aimed to investigate the effects of H 2 -rich water (HW) consumption in healthy adults through the extensive analyses of antioxidant capacity, peripheral blood mononuclear cell (PBMC) subsets and their transcriptome profile and to compare the effects of HW consumption with those of plain water (PW) consumption.

Participants and baseline characteristics

The flow diagram of the participants throughout the study is presented in Fig.  1 . A total of 158 participants were assessed for eligibility according to the inclusion and exclusion criteria. 41 participants were found to be eligible and were included in the study. They were randomly assigned to either the PW group ( n  = 19) or the HW group ( n  = 22). Out of 3 participants who withdrew from the study, 1 participant in PW group dropped out before starting the intervention, and 2 participants in HW group dropped out on the 4th day and the 10th day. As a result, a total of 38 participants successfully completed the 4-week intervention and were included in the final analysis ( n  = 18 in PW group; n  = 20 in HW group) (Fig.  1 ).

Flow diagram of the participants throughout the study.

As shown in Table 1 , there were no statistical differences in age, height, weight, BMI and daily plain water intake at baseline between the PW and HW groups (all P  > 0.05).

Antioxidant capacity and oxidative damages

Four-week consumption of both plain water and hydrogen-rich water increased serum biological antioxidant potential (BAP) (Δ = 194.4 ± 315.4 μmol/L, P  < 0.05 in PW; Δ = 297.8 ± 274.2 μmol/L, P  < 0.001 in HW) (Table 2 ). Although there was no significant difference in the between-group comparison of PW versus HW in the total population ( P  = 0.267) (Table 2 ), participants who were over 30 yrs old showed a significant increase in BAP by drinking hydrogen-rich water but not plain water, and the difference in the changes was significant ( P  = 0.028) (Fig.  2 ). On the contrary, no significant effect of hydrogen rich water on BAP was found in the younger group (< 30 y) ( P  = 0.534) (Fig.  2 ).

Changes from baseline in serum BAP by age (< 30 y and ≥ 30 y). Data are presented as means ± SEMs. Significant differences between baseline and week 4 within each group were determined with the use of a paired t test. P values were obtained with the use of simple main effects analysis and P  < 0.05 was considered statistically significant. ( A ) Within the participants aged < 30 y, there was no significant difference between PW group ( n  = 10) and HW group ( n  = 10) for the change in BAP ( P  = 0.534). ( B ) HW group aged ≥ 30 y ( n  = 10) showed a greater increase in BAP compared with PW group aged ≥ 30 y ( n  = 8) ( P  = 0.028). PW, plain water; HW, H 2 -rich water; BAP, biological antioxidant potential.

Oxidative stress in serum assessed by the level of derivatives of reactive oxygen (d-ROMs) was not affected by the 4-week intervention (all P  > 0.05) (Table 2 ). The levels of 8-Oxo-2′-deoxyguanosine (8-OHdG), a marker for DNA damage, significantly decreased in both groups (Δ = − 0.94 ± 1.44 ng/mL, P  < 0.05 in PW; Δ = − 1.32 ± 1.05 ng/mL, P  < 0.001 in HW), but with no statistical difference between the PW and HW groups (all P  > 0.05) (Table 2 ).

Apoptosis of PBMCs and blood immune cell population profiles

At the baseline, there was no significant difference between two groups in the frequencies of apoptotic cells in the blood ( P  = 0.606) (Fig.  3 ). After the 4 week of trial, however, HW group showed a significantly lower percentage of PBMC apoptosis compared with PW group ( P  = 0.036) (Fig.  3 ).

Representative flow cytometric data ( A ) and frequencies of apoptotic cells (Annexin V + DAPI + ) at baseline and week 4 ( B ). Data are presented as means ± SEMs. Significant differences between PW group ( n  = 14) and HW group ( n  = 15) at baseline were determined with the use of an unpaired t test or a Mann–Whitney U test, and those at week 4 were determined with a general linear model adjusting for the value at baseline as a covariate. PW, plain water; HW, H 2 -rich water.

Subsets of PBMCs were profiled with the antibodies specific for cell surface markers including CD4, CD8, CD20, CD14, and CD11b. PW and HW groups presented similar patterns of change in CD4 + (Δ = − 3.5 ± 4.8%, P  < 0.01 in PW; Δ = − 2.4 ± 3.6%, P  < 0.01 in HW), CD8 + (Δ = − 4.8 ± 2.1%, P  < 0.001 in PW; Δ = − 4.5 ± 2.6%, P  < 0.001 in HW) and CD11b + cells (both P  > 0.05) (Table 3 ). Although the frequency of CD20 + cell increased in the HW group compared to baseline values (Δ = 1.5 ± 2.5% and P  < 0.05), there were no significant differences between the HW and PW groups ( P  = 0.900) (Table 3 ). It is notable that the change in the frequency of CD14 + cells in the HW group was significantly different from the change in the PW group ( P  = 0.039) (Table 3 ) .

Transcriptome profiles of PBMCs

In order to elucidate molecular mechanisms by which hydrogen-rich water consumption affects the apoptosis and immune cell profiles of PBMC, RNA-sequencing analysis in a genome-wide scale was carried out using total sets of RNAs from 6 individuals that included three randomly selected samples per group. A total of 605 differentially-expressed genes (DEGs) between the HW and PW groups were identified as described in “ Methods ”. Hierarchical clustering analysis showed transcriptomes of HW were readily distinguishable from those of PW (Fig.  4 A). To gain insights into functional implications of the altered gene expression profiles caused by hydrogen water, the DEGs were categorized by physiological functions and a significance of the enrichment of each category was tested by Fisher’s exact test. Interestingly, the top 5 significant categories were Inflammatory response, Immune cell trafficking, Hematological system development and function and Infectious diseases and immunological disease (Fig.  4 B). Within the top significant category, Inflammatory response, it was of interest that genes involved in TLR- NF-κB signaling were greatly reduced in expression. They included a series of toll-like receptors and key mediator molecules such as TLR1, TLR2, TLR4, TLR6, TLR7, TLR8, TLR9 and MYD88. In addition, transcription of intracellular proteins involved in NF-κB signaling including NFKB1, NLRP12 and MAP3K1 and, therefore, down-stream genes such as FOS and RELB were significantly reduced in the HW group (Fig.  4 C). Also, we investigated the expression levels of genes responsive to NF-κB activation and those encoding pro-inflammatory cytokines and their receptors. Consequently, we observed that the HW group had the significantly lower expression levels in IL1B, IL8, IL6R, and TNFRSF10B than the PW group (Fig.  4 D).

Transcriptome profiles of peripheral blood mononuclear cells at week 4. ( A ) Hierarchical clustering analysis of DEGs ( B ) Top 5 biological functional categories were discovered within DEGs by IPA. Statistical significance was calculated by the Fisher’s exact test and noted as a log ( P -value). ( C ) Heat maps of expression levels of key genes related to toll like receptor and NF-κB signaling ( D ) HW group ( n  = 3) presented the lower expression levels in IL6R and NF-κB responsive genes including IL1B, IL8 and TNFRSF10B, compared with PW group ( n  = 3). Data are presented as means ± SEMs. Significant differences between PW and HW groups were determined with the use of an unpaired t test. PW, plain water; HW, H 2 -rich water; DEG, differentially expressed genes; IPA, Ingenuity Pathway Analysis; RPKM, reads per kilobase million.

The effects of H 2 -rich water on antioxidant system have been tested largely within in vitro or animal models, with limited human data from few patient studies allowing substantiation of the beneficial roles of the water 19 , 20 , 21 . To the best of our knowledge, this is the first randomized clinical trial investigating the antioxidant activities of H 2 -water in heathy subjects, especially through a comprehensive analysis of oxidative stress markers, blood immune cell profiles, and the genome-scale gene expression. Four-week consumption of H 2 -water induced a substantial increase in the antioxidant capacity and a decrease in oxidative stress of DNAs, although there was no significance found in the comparison of an intervention (H 2 -water) and the placebo (plain water) group. These observations that H 2 -water showed some potential to have antioxidant activity, prompted us to further examine the effect on the apoptosis of peripheral blood cells in each subject, since even small changes in oxidative stress might be sufficient enough to initiate the apoptotic process. We found that the frequencies of apoptotic cells were significantly reduced by H 2 -water. In addition, flow cytometry analysis of peripheral blood showed that H 2 -water significantly reduced frequencies of circulating CD14 + cells. Interestingly, RNA-sequencing analyses identified a transcriptional network of inflammatory response as the most significant biological function modulated by H 2 -water. It greatly suppressed the expressions of genes involved in TLR-NF-κB signaling, as a result, the transcript levels of pro-inflammatory cytokines were significantly decreased.

There is extensive experimental evidence that oxidative stress can disrupt the cellular function by deforming the nucleic acids 22 ; the oxidative DNA damage can be cytotoxic or mutagenic, and has been related to disease pathogenesis 23 . One of the most predominant forms of endogenous DNA lesion is 8-OHdG, which is formed by the addition of hydroxyl radical to the deoxyguanosin 24 . Thus, 8-OHdG has been widely used as a hallmark of oxidative stress and elevated levels of 8-OHdG might be a risk factor for cancer, atherosclerosis, and diabetics 25 . It is noteworthy that the concentration of 8-OHdG decreased to 35% of the baseline levels in the HW group, albeit no significance was found because of the 52% reduction in the PW group as well. Ishibashi et al . also observed that patients with rheumatoid arthritis showed a significant reduction in the levels of urinary 8-OHdG after intake of 530 mL/d of H 2 -water for 4 weeks 17 . The hydrogen-water has been shown to reduce DNA oxidation in animal model studies. H 2 -rich water treatment to rats inhibited an age-dependent increase in serum 8-OHdG levels 26 . The protective effect of H 2 against DNA oxidative injury was also enhanced in a rabbit model of steroid-induced osteonecrosis, as revealed by quantifying 8-OHdG-positive haematopoietic cells 27 . Similarly, an intraperitoneal injection of H 2 -rich saline to rats was effective in decreasing the number of 8-OHdG-positive myocardial cells after inducing cardiac I/R injury 28 . One possible mechanistic explanation for the suppressive effect of HW on the production of 8-OHdG is that inert hydrogen reacts with hydroxyl radical 9 . However, further mechanistic studies are needed to identify whether a direct interaction between the hydroxyl radical and hydrogen exists when molecular hydrogen is administered via oral ingestion of H 2 -rich water. Unlike 8-OHdG, many varied molecules are involved in lipid peroxidation, including peroxy, alkoxy, alkyl radicals, ozone, and sulfur dioxide as well as the hydroxyl radical 23 . It has been known that H 2 selectively removes the hydroxyl radicals without affecting other ROS 29 ; thus, it is not surprising that no changes in d-ROMs were observed during the intervention.

Aging is generally characterized by a state in which systemic oxidative stress is elevated and/or the antioxidant defense system is altered, indicating dysregulation of redox balance and the accumulation of oxidative damages 30 . We therefore assumed that the effects of H 2 -water might vary with the age of participants. Although there was no difference in serum biological antioxidant potential between the intervention and placebo groups in the population as a whole, stratifying for age showed a significant increase in antioxidant capacity in the older group aged ≥ 30 y. The younger age group (< 30 y) showed no difference between H 2 -water and placebo groups. This finding implies that H 2 -water could exert antioxidant capacity-promoting benefits more in older adults than in the young.

Apoptosis is one of the consequences resulting from excessive ROS generation 31 . As the mitochondrial respiratory chain is the major source of endogenous ROS, mitochondrial DNA, proteins and lipids are susceptible to ROS attack, and these biomolecular damages beyond the capacity of repair can lead to programmed cell death 32 . Excessive destruction of normal cells constitutes a major cause of aging 33 , diabetes 34 and neurodegenerative diseases 35 . Surprisingly, the HW group showed a lower percentage in apoptotic PBMC at week 4 compared with the PW group. This suggested that HW consumption was effective in preventing severe cellular damages. Because hydrogen molecules have small size and low molecular weight enough to diffuse across the cellular membrane and enter intracellular compartments, H 2 may have directly suppressed these severe damages 36 . The anti-apoptotic function of H 2 has been reported by others in animal model studies such as ischemia/reperfusion-induced rats 37 and hypoxia–ischemia rats 38 . In addition, a human study of an uncontrolled clinical trial in patients with potential metabolic syndrome demonstrated an anti-apoptotic effect of HW consumption in endothelial cells 16 . The decrease in apoptosis in the present study may have been linked to the decrease in the frequency of CD14 positive PBMCs. CD14 is mainly expressed on the surface of human circulating monocytes 39 . Oxidatively-stressed cells induce CD14 + monocytes to migrate around them for apoptotic cell clearance 40 , and recruited monocytes successfully phagocytose the dying cells 41 . Thus, alleviation of oxidative stress resulted in a decrease in cell damage, which, in turn, decreased the frequency of circulating monocytes.

Oxidative stress and inflammation are tightly linked each other. Immune cells are stimulated by the ROS-damaged biomolecules to promote an inflammatory response 3 , 4 . Some ROS directly activate redox-sensitive proteins and transcription factors including mitogen-activated protein kinase (MAPK) and NF-κB. They also trigger the production of pro-inflammatory cytokines including IL-1 and IL-6 42 , 43 . Inflammatory cells generate ROS, thereby further enhancing these responses. Hydroxyl radicals act as a strong messenger for NF-κB activation which is pivotal in inflammation, consequently, radical-scavenging contributes to anti-inflammatory effects 44 . As shown in the present study, H 2 -water consumption remarkably down-regulated the NF-κB signaling pathway. H 2 also suppressed NF-κB-regulated genes in the healthy mouse liver 45 . In animal studies with models of inflammation, H 2 -administration effectively decreased the levels of pro-inflammatory cytokines such as IL-1, IL-6, and TNF-α 46 , 47 , 48 , 49 . In addition, H 2 has been reported to generate modified phospholipid, an antagonist of oxidized phospholipids, resulting in a decline in Ca 2+ signaling and the Ca 2+ -dependent nuclear factor of activated T cells (NFAT) pathway which induces the production of pro-inflammatory cytokines 50 .

In the present study, 1.5 L of water was consumed daily by all participants whether they were in the intervention or placebo groups. Based upon an individual’s self-records on habitual water intake that was analyzed before participation, this intervention study prompted participants to drink 300 mL more water on average compared to their usual intake. Therefore, this increment in water intake might generate beneficial effects on the physiology of immune system, which might be attributable to the observation that biological antioxidant capacity was enhanced and oxidative DNA damage was reduced even by plain water. Some limitations of the study include a relatively short-term intervention, and thus the results cannot address the long-term effect of H 2 -water. In addition, study participants were mostly recruited from the Seoul National University and local residents, and therefore may not be representative of the general population of healthy adults. Finally, the study population number may have been not large enough to yield significant difference in blood oxidative stress markers.

In conclusion, this work presents, to our knowledge, the first double-blind placebo-controlled comprehensive study investigating the effects of H 2 -water in healthy adults. 1.5 L of H 2 -water intake for 4 weeks reduced cell death and inflammatory responses by modulating transcriptional networks of TLR-NFκB signaling. In addition, it may promote biological antioxidant capacity for adults > 30 yrs more than younger individuals.

Participants

158 individuals were recruited to the study which was advertised on the school portal website and bulletin boards. They were assessed for eligibility according to the following inclusion criteria: men and women aged 20–59 y; no medical history of acute or chronic diseases; and average daily consumption of water ranging from 500 to 2,500 mL. Exclusion criteria were as follows: consumption of beverages including coffee, tea, soft drinks and alcohol > 500 mL per day; consumption of alcohol containing beverages > 2 days per week; regular use of antioxidant supplements including vitamins and minerals within the last 3 months; and habits of smoking or strenuous exercise. A total of 117 volunteers were excluded based on the following reasons: 36 persons did not match our consumption standard of pure water (500–2,500 mL/day); 35 persons were consuming extra beverages (not pure water) over 500 mL/day; 29 persons had a history of regular use of antioxidant supplements within the last 3 months; 7 persons had a smoking habit; and 17 persons had a high level of physical activity according to International Physical Activity Questionnaire.

Study design

This study was a 4-week, parallel-designed, randomized, double-blind, and placebo-controlled trial. Eligible participants were randomly assigned to either a plain water group (PW group) or a H 2 -rich water group (HW group), and the random assignment was stratified by sex and age (< 30 y and ≥ 30 y) with the use of an online randomization service (Sealed Envelope, London, UK). At baseline and after the trial, blood samples were collected when the participants were at rest. Participants in both the PW and HW arms were advised to maintain their usual diet and physical activities and to avoid taking any antioxidant supplements throughout the experimental period. All investigators and staffs involved in the random assignment, measurement and assessment of outcomes were blinded to the allocation. This study was conducted at the Department of Food and Nutrition in Seoul National University between Aug and Oct 2016, and was approved by the Institutional Review Board of Seoul National University (IRB No. 1606/001-012). All methods were performed in accordance with the relevant guidelines and regulations. This trial was registered at the Clinical Research Information Service (CRIS) on April 12th, 2019 (Registry No. KCT0003763). Written informed consent was provided by all participants prior to inclusion in the study.

Water intervention

Commercially available H 2 -rich water (Koreahydrogenwater Corp., Seoul, Korea) and plain water (Coway Co., Ltd, Seoul, Korea) were used. The hydrogen concentration of the H 2 -rich water was 0.753 ± 0.012 mg/L when measured using the dissolved H 2 analyzer (Orbisphere 3,654 portable analyzer; Hach, Switzerland, Geneva). A label was attached to each container and only information, such as the participant’s code and the date of manufacturing were provided on it. Each participant was provided daily with 3 bottles of 500 mL water, either PW or HW. All participants were instructed to finish the 500 mL of water bottle within an hour after opening the bottle to minimize a loss of dissolved H 2 . They were not allowed to drink any other additional water with an exception of coffee, tea, soft drinks and alcoholic beverages, but the total consumption of such extra drinks was controlled to ≤ 500 mL per day to minimize the variation in total beverage consumption. Participants were encouraged to record a daily history of water consumption, and any extra beverages if ever consumed. The records were reviewed 2 times a week to enhance their compliance to the study. The average compliances (%) for the HW group and the PW group were 99.2 ± 1.7 and 99.3 ± 1.1, respectively, with no statistical difference between the two groups ( P  = 0.762), as determined by Mann–Whitney U test. The analysis of extra beverage consumption showed no statistical difference between the two groups (HW group: 159.0 ± 82.0 mL/day; PW group: 143.0 ± 60.1 mL/day; P  = 0.090, by an unpaired t test).

Blood sampling

The first visit took place on the day before starting the intervention, and the second one was done on the day subsequent to the last day of the intervention. On each visit, participants filled in a questionnaire containing the questions about daily dietary intake and physical activities. Fasting venous blood samples from antecubital fossa were collected into 8-mL serum separator tubes (BD Biosciences, Franklin Lakes, NJ, USA), 8-mL EDTA-containing tubes (BD Biosciences), and BD vacutainer mononuclear cell preparation tubes with sodium citrate (BD Biosciences). Upon collection, plasma and serum samples were aliquoted in 1.5 mL ep-tubes (Eppendorf, Hamburg, Germany) and were frozen at − 80 °C for a later analysis.

Measurements

Antioxidant capacity was determined by measuring BAP in serum using a BAP test (BAP Kit; Diacron Srl., Grosseto, Italy). Oxidative stress in serum was assessed by the level of ROS-derived hydroperoxides measured using a diacron reactive oxygen metabolites kit (Diacron Srl.). 8-OHdG, an indicator of DNA damage by oxidative stress, was measured in serum with the use of an enzyme-linked immunosorbent assay (8-OHdG Check ELISA; Jaica, Fukuroi, Japan) in accordance to the manufacturer’s instructions.

Apoptosis of PBMCs

Annexin V staining was performed using PE-conjugated anti-annexin V antibody (eBioscience) in annexin V binding buffer (10 mM HEPES [pH7.4], 140 mM NaCl. 2.5 mM CaCl 2 ) at RT for 15 min. DAPI (4′,6-diamidino-2-phenylindole; Sigma-Aldrich) staining was used for excluding dead cells and apoptotic analysis. Frequencies of apoptotic cells were analyzed using BD LSRFortessa (BD Biosciences, San Jose, CA, USA).

Immune cell population profiles

PBMCs were isolated from the whole blood by density-gradient centrifugation using Ficoll-Paque PLUS density gradient media (GE healthcare, Songdo, Korea). PBMCs were stained with Alexa Fluor 488-conjugated anti-human CD4 (OKT4; eBioscience, San Diego, CA, USA), PE-conjugated anti-human CD8 (3B5; eBioscience), APC-Cy7-conjugated anti-human CD20 (B-Ly-1; eBioscience), APC-Cy7-conjugated anti-human CD11b (ICRF44; BD Biosciences, San Jose, CA, USA), APC-conjugated anti-human CD14 (61D3; eBioscience) antibodies in FACS buffer (0.1% bovine calf serum and 0.05% sodium azide in 1 × PBS [phosphate buffered saline]) at 4 °C for 30 min. Profiles of each populations were analyzed by flow cytometry with FlowJo software (TreeStar, Ashland, OR, USA).

Transcriptome profiles of PBMCs–RNA-next generation sequencing

PBMCs were isolated immediately after the blood collection with the use of BD vacutainer mononuclear cell preparation tubes with sodium citrate (BD Biosciences) and then total RNA was extracted from PBMCs (RNAqueous-4PCR Kit; Ambion, TX, USA). Quality and concentration of extracted total RNA were assessed using Agilent 2,100 Bioanalyzer (Agilent Technologies, CA, USA). Out of the samples with RNA integrity number (RIN) greater than 8, a total of 6 samples (3 samples per a group) were randomly selected to be sequenced. Subsequently, intact mRNA was captured from the total RNA with the use of Dynabeads mRNA DIRECT Micro Kit (Ambion). Total mRNA samples were depleted of 5S, 5.8S, 18S, and 28S ribosomal subunits up to 99.9% using RiboMinus Eukaryote System v2 (Life Technologies, Carlsbad, CA, USA). Absence of ribosomal peaks was confirmed using Bioanalyzer and RNA 6,000 Pico Kit (Agilent Technologies). Barcoded cDNA libraries were prepared from the ribo-depleted mRNA samples and constructed with the use of reagents in Ion Total-RNA Seq Kit v2 (Life Technologies). First, the mRNA was fragmented with RNase III at 37 °C for 3 min. The fragmented RNA was purified on nucleic acid-binding beads and hybridized with Ion Adaptor Mix v2. Subsequently, ligation was performed at 30 °C for 1 h. The adaptor-ligated libraries were pre-incubated with a reverse transcription primer at 70 °C for 10 min and then converted to cDNA by reverse transcription at 42 °C for 30 min. The cDNA libraries were purified on nucleic acid-binding beads and then amplified by PCR using barcoded primers (Ion Xpress RNA-Seq Barcode 01–16 Kit; Life Technologies). After the bead-purification, molarity of the final library was determined using Bioanalyzer and High Sensitivity DNA Kit (Agilent Technologies). Whole transcriptome libraries were diluted to 100 pM using Bioanalyzer and amplified on Ion Sphere Particles (ISPs) by emulsion PCR with the use of Ion One Touch 2 system (Life Technologies) and Ion PI Hi-Q OT2 200 Kit (Life Technologies). Enrichment of template-positive ISPs were performed using Ion OneTouch Enrichment System (ES) (Life Technologies) where biotinylated adaptor sequences were selected by binding to streptavidin beads. Subsequently, the template-positive ISPs were sequenced with the use of Ion PI Hi-Q Sequencing 200 Kit (Life Technologies). Sequencing primers were annealed to the template fragments attached to ISPs, and the template positive ISPs samples were loaded on a chip of Ion PI Chip Kit v3 (Life Technologies) and incubated with polymerase. Finally, the chip was placed on Ion Proton System (Life Technologies) for sequencing working on the principal that hydrogen ion release was detected when new nucleotides were incorporated into the growing DNA template 51 . All procedures were performed according to the manufacturer's instructions.

Bioinformatics analysis of RNA sequences

Raw reads generated by the sequencer were trimmed and filtered. Trimming was performed to remove the adapter sequence and lower-quality 3′ ends with low quality scores. Read filtering was carried out to remove adapter dimers, reads lacking a sequencing key and polyclonal reads. High quality reads were mapped and aligned with the computational pipeline of Bowtie 2 and TopHat 52 . After mapping and aligning, the resulting BAM files were imported into Partek Genomics Suite v6.6 (Partek Inc., Saint Louis, MI, USA) and converted into gene transcript levels as reads per kilobase of exon per million mapped reads (RPKM) with the use of a mixed-model approach. DEGs were identified with a fold-change threshold (greater than 2 or less than − 2) and P value ( P  < 0.01). Genes that passed our statistical criteria were analyzed with the bioinformatics software Ingenuity Pathway Analysis (IPA; www.ingenuity.com ). Hierarchical clustering analysis and biological classification analysis was performed. Fisher’s exact test was used to test a significance for the enrichment of specific biological processes in the set of DEGs.

Statistical analysis

Statistical analysis was performed with the use of SPSS version 23 for Macintosh (IBM Corp., Chicago, IL, USA). A sample size was calculated based on a previous study 17 with an α = 0.05 and a power of 80%. All data were tested for normality before selecting the appropriate statistical method. General characteristics at baseline were analyzed on the basis of an unpaired t test or Mann–Whitney U test to identify whether there were statistical differences between groups. A paired t test or a Wilcoxon signed-rank test was used for within-group comparisons between baseline and week 4. The changes from baseline to week 4 were compared between PW and HW groups on the basis of a general linear model with an adjustment for the value at baseline as a covariate. We conducted a two-way ANOVA with an adjustment for the value at baseline as a covariate to determine the interaction between the effects of treatment (PW or HW) and age (< 30 y or ≥ 30 y) regarding the changes from baseline to week 4 in BAP, d-ROMs, 8-OHdG, PBMC apoptosis and subsets. When a significant interaction was discovered, simple main effects analysis was performed. P  < 0.05 was considered statistically significant.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

This work was supported by Coway Co., Ltd., & the National Research Foundation of Korea (NRF-2018R1D1A1B07048023).

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Minju Sim, Chong-Su Kim, Woo-Jeong Shon & Dong-Mi Shin

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The authors’ responsibilities were as follows—D.-M.S. and E.Y.C.: designed the research; M.S. and C.-S.K.: conducted the research; M.S., W.-J.S. and Y.-K.L.: collected and analyzed data; M.S.: prepared the manuscript; D.-M.S.: reviewed and edited the manuscript.

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Sim, M., Kim, CS., Shon, WJ. et al. Hydrogen-rich water reduces inflammatory responses and prevents apoptosis of peripheral blood cells in healthy adults: a randomized, double-blind, controlled trial. Sci Rep 10 , 12130 (2020). https://doi.org/10.1038/s41598-020-68930-2

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DOI : https://doi.org/10.1038/s41598-020-68930-2

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The research entitled "Future malaria environmental suitability in Africa is sensitive to hydrology" was funded by the Natural Environment Research Council and is published today (9 May 2024) in the journal Science .

Dr Mark Smith an Associate Professor in Water Research in the Leeds' School of Geography and lead author of the study said: "This will give us a more physically realistic estimate of where in Africa is going to become better or worse for malaria.

"And as increasingly detailed estimates of water flows become available, we can use this understanding to direct prioritisation and tailoring of malaria interventions in a more targeted and informed way. This is really useful given the scarce health resources that are often available."

Malaria is a climate-sensitive vector-borne disease that caused 608,000 deaths among 249 million cases in 2022.

95% of global cases are reported in Africa but reductions in cases there have slowed or even reversed in recent years, attributed in part to a stall in investments in global responses to malaria control.

The researchers predict that the hot and dry conditions brought about by climate change will lead to an overall decrease in areas suitable for malaria transmission from 2025 onwards.

The new hydrology-driven approach also shows that changes in malaria suitability are seen in different places and are more sensitive to future greenhouse gas emissions than previously thought.

For example, projected reductions in malaria suitability across West Africa are more extensive than rainfall-based models suggested, stretching as far east as South Sudan, whereas projected increases in South Africa are now seen to follow watercourses such as the Orange River.

Co-author of the study Professor Chris Thomas from the University of Lincoln said: "The key advancement is that these models factor in that not all water stays where it rains, and this means breeding conditions suitable for malaria mosquitoes too can be more widespread -- especially along major river floodplains in the arid, savannah regions typical of many regions in Africa.

"What is surprising in the new modelling is the sensitivity of season length to climate change -- this can have dramatic effects on the amount of disease transmitted."

Simon Gosling, Professor of Climate Risks & Environmental Modelling at the University of Nottingham, co-authored the study and helped to coordinate the water modelling experiments used in the research. He said: "Our study highlights the complex way that surface water flows change the risk of malaria transmission across Africa, made possible thanks to a major research programme conducted by the global hydrological modelling community to compile and make available estimates of climate change impacts on water flows across the planet.

"Although an overall reduction in future risk of malaria might sound like good news, it comes at a cost of reduced water availability and a greater risk of another significant disease, dengue."

The researchers hope that further advances in their modelling will allow for even finer details of waterbody dynamics which could help to inform national malaria control strategies.

Dr Smith added: "We're getting to the point soon where we use globally available data to not only say where the possible habitats are, but also which species of mosquitoes are likely to breed where, and that would allow people to really target their interventions against these insects."

• Infectious Diseases
• Pests and Parasites
• Environmental Issues
• Environmental Awareness
• Global climate model
• Climate model
• Infiltration (hydrology)
• Pest (animal)
• IPCC Report on Climate Change - 2007
• Consensus of scientists regarding global warming
• Climate engineering

Story Source:

Materials provided by University of Leeds . Note: Content may be edited for style and length.

Journal Reference :

• Mark W. Smith, Thomas Willis, Elizabeth Mroz, William H. M. James, Megan J. Klaar, Simon N. Gosling, Christopher J. Thomas. Future malaria environmental suitability in Africa is sensitive to hydrology . Science , 2024; 384 (6696): 697 DOI: 10.1126/science.adk8755

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