Drinking Water: Benefits, Quality, Daily Needs and the Risks of Too Little

Water makes up roughly 50 to 60 percent of an adult's body weight. It carries nutrients, regulates temperature, cushions joints and organs, and lets the kidneys clear waste. Because the body cannot store much of it, we must replace what we lose every day through urine, sweat, breath and stool. This article explains why adequate water matters, what makes drinking water safe according to the World Health Organization (WHO), how much different people need, and what happens when intake falls short. Numbered references in square brackets point to the Bibliography at the end.

1. Ten Benefits of Drinking Adequate Water

1. Regulates body temperature. Sweating is the body's main cooling system, and it depends on a steady water supply. Adequate hydration helps maintain normal temperature regulation during heat and exercise [3, 14].

2. Supports physical performance. Even a loss of around 2 percent of body weight through sweat can reduce endurance and performance, which is why sports medicine bodies advise planned fluid replacement during prolonged exercise [8, 14].

3. Sharpens concentration and mood. Controlled studies in healthy young adults found that mild dehydration impaired attention, increased fatigue and headache, and worsened mood. Women in particular reported more tension and difficulty concentrating [11, 12].

4. Helps the kidneys and may lower stone risk. Higher urine volume dilutes the minerals that form kidney stones. In a five-year randomized trial, people with recurrent calcium stones who drank enough to produce about 2 litres or more of urine a day had markedly fewer recurrences than those who did not [9].

5. Reduces recurrent urinary tract infections in some women. A randomized trial in premenopausal women with frequent infections found that drinking an extra 1.5 litres of water a day reduced the number of recurrences [10].

6. Keeps digestion and bowels regular. Water softens stool and helps food move through the gut. Low fluid intake is a recognized contributor to constipation, particularly alongside low fibre intake [13].

7. Eases some headaches. Dehydration is a known headache trigger. In a randomized trial of people with recurrent headaches, increased water intake improved headache-related quality of life, although the effect on frequency was modest [15].

8. Supports healthy weight management. In a trial of middle-aged and older adults on a calorie-reduced diet, those who drank water before meals lost more weight over 12 weeks than those who did not [16]. Replacing sugary drinks with water also cuts calories without effort.

9. May support long-term kidney and metabolic health. One trial in chronic kidney disease found that coaching to raise water intake did not slow kidney function decline [7], so more water is not a treatment for every condition. Observational studies, however, link higher urine volume with a slower fall in kidney function in the general population [6], and low water intake with a higher risk of developing high blood sugar [17]. These are associations, not proof of cause.

10. Keeps skin, joints and tissues functioning. Water is the main component of blood, lymph, joint fluid and saliva. It carries oxygen and nutrients to cells and removes waste. A large NIH-supported analysis found that adults with higher serum sodium (a marker of lower hydration) in midlife had higher odds of chronic disease and earlier biological ageing, though again this shows association rather than causation [18].

2. Quality of Drinking Water According to the WHO

The WHO's Guidelines for Drinking-water Quality (GDWQ) are the world's main reference on the subject. The current version is the fourth edition, now updated through a third addendum, and it is the basis for national regulations and standards worldwide [1, 2]. A few points are worth understanding.

The Guidelines are not a single universal list of limits. They recommend locally relevant, health-based targets, preventive risk management from catchment to consumer through Water Safety Plans, and independent surveillance to check that standards are actually being met [1]. Countries adapt the guideline values into their own standards. India's IS 10500, for example, is set by the Bureau of Indian Standards [19].

Microbiological safety comes first. Disease-causing bacteria, viruses and protozoa are the biggest drinking-water risk globally. The WHO's core verification target is that Escherichia coli (or thermotolerant coliforms) must not be detectable in any 100 mL sample of water intended for drinking [1].

Disinfection and clarity. To make disinfection effective, turbidity (cloudiness) should ideally be kept below 1 NTU. Where chlorine is used, a free residual of at least 0.2 mg/L at the point of delivery is generally recommended, and the health-based guideline value for chlorine is 5 mg/L [1].

Chemical guideline values. The Guidelines give health-based values for many substances. Selected examples for long-term exposure [1]:

• Arsenic: 0.01 mg/L (10 µg/L)

• Lead: 0.01 mg/L, with the goal of keeping it as low as reasonably achievable

• Fluoride: 1.5 mg/L (protects against dental and skeletal fluorosis)

• Nitrate: 50 mg/L as nitrate (mainly protects bottle-fed infants from methaemoglobinaemia)

• Nitrite: 3 mg/L (short-term exposure)

• Cadmium: 0.003 mg/L

• Copper: 2 mg/L

• Inorganic mercury: 0.006 mg/L

Guideline values are revised as evidence changes, so check the current edition before relying on a specific figure.

Acceptability: taste, odour and appearance. Water can be safe yet unpleasant, or pleasant yet unsafe. People who dislike the taste of safe water may switch to unsafe sources, so the WHO also addresses acceptability. Values such as a pH of roughly 6.5 to 8.5 and total dissolved solids below about 600 mg/L for good palatability are operational or aesthetic guides, not health limits [1].

Packaged, travel and small-supply water. The Guidelines include sections on packaged drinking-water, safe water for travellers and small community supplies, where treatment and testing are often hardest to maintain [1, 2].

What this means for you. Water from a reliable, treated and tested supply is generally safe. If your source is a private well, a tube well or an untreated supply, have it tested for microbes and for locally relevant chemicals such as arsenic, fluoride, nitrate or iron. Boiling, filtration and disinfection can make microbially unsafe water safe, but not all household treatments remove chemical contaminants.

3. How Much Water Should You Drink?

No single number fits everyone. Authorities usually state recommendations as total water intake, which includes drinking water, other beverages and the water in food. Food typically supplies around 20 percent of the total, so the amount you need to actually drink is lower than the headline figure [3, 4].

Adults: two reference points

• EFSA (Europe): 2.0 litres per day for adult women and 2.5 litres for adult men, in moderate temperatures and with moderate activity [3].

• US National Academies: about 2.7 litres for women and 3.7 litres for men, derived from the intakes of healthy, adequately hydrated people. This covers sedentary people in temperate climates, and the panel noted that thirst-driven drinking meets the needs of most healthy people [4].

The gap between the two reflects different methods, not a scientific disagreement. Both are adequate-intake estimates rather than strict requirements [5].

By age and life stage (total water, from drink and food)

The EFSA values [3]:

• Infants 6 to 12 months: 0.8 to 1.0 L

• Children 1 to 3 years: 1.1 to 1.2 L

• Children 4 to 8 years: about 1.6 L

• Ages 9 to 13: about 1.9 L (girls) and 2.1 L (boys)

• Age 14 and over: 2.0 L (women) and 2.5 L (men)

• Pregnancy: add about 0.3 L

• Breastfeeding: add about 0.7 L

The US National Academies set higher values, for example about 1.7 L for ages 4 to 8, about 3.3 L for boys aged 14 to 18, 3.0 L in pregnancy and 3.8 L during lactation [4]. In infants under six months, breast milk or formula supplies all the water needed, and extra water should not be given unless a doctor advises it.

Older adults. The sense of thirst weakens with age, and kidneys concentrate urine less efficiently, so older people can become dehydrated without feeling thirsty. Regular drinking through the day is sensible unless a doctor has limited fluids [5, 13].

By body weight

Official bodies do not publish a single per-kilogram rule for healthy adults, but a common practical estimate is about 30 to 35 mL per kg of body weight per day of total fluid. For a 60 kg adult that is roughly 1.8 to 2.1 L, and for an 80 kg adult roughly 2.4 to 2.8 L. This is a rule of thumb, not an official standard, and it lands in the same range as the reference values above. Larger people lose more water through the skin and breath and have greater metabolic needs, which is why heavier adults generally need more. For hospital-style calculations in children, clinicians use weight-based formulas, so a child who is ill should be assessed by a doctor rather than given a calculated amount at home.

By place and conditions

• Hot or humid climates: Sweat losses can raise needs substantially. The National Academies note that very active people exposed to heat often need 6 litres or more of total water per day [4].

• Exercise: Needs depend on sweat rate, which varies widely between people. The American College of Sports Medicine advises drinking enough to avoid losing more than about 2 percent of body weight during exercise, while not drinking more than you sweat out [14].

• High altitude and cold, dry air: Breathing dry air raises water loss from the lungs, and cold or altitude can blunt thirst, so intake often needs to rise even though you feel less need to drink.

• Air-conditioned and heated interiors: Low humidity can modestly increase insensible water loss.

• Illness: Fever, vomiting and diarrhoea sharply raise needs, and oral rehydration solution is more effective than plain water for replacing lost salts.

Practical guidance

For most healthy people, drinking to thirst and checking urine colour (pale straw is a good sign; dark yellow suggests you need more) works well [4, 5]. Tea, coffee, milk, soups and water-rich fruit and vegetables all count toward total intake. There is no convincing evidence that moderate caffeine intake causes a net water deficit [4].

More is not always better. Drinking very large volumes in a short time, especially during long endurance events, can dilute blood sodium and cause exercise-associated hyponatraemia, which can be dangerous [20]. People with kidney, heart or liver disease, or on diuretics, often have prescribed fluid limits and should follow their doctor's advice rather than general figures.

4. Harmful Effects of Not Drinking Enough Water

Dehydration is a loss of body water that disturbs normal function. Clinical consensus recognizes that it ranges from mild to life-threatening [21].

Early and mild effects:

• Thirst, dry mouth and dark, strong-smelling urine in smaller amounts

• Headache, tiredness and reduced alertness

• Poorer concentration, memory and mood, shown in controlled studies even at 1 to 2 percent loss of body water [11, 12]

• Reduced exercise capacity and slower recovery [8, 14]

• Constipation [13]

Moderate to severe effects:

• Dizziness, rapid heartbeat, low blood pressure and fainting

• Muscle cramps and, in hot conditions, heat exhaustion and heat stroke

• Confusion, extreme weakness and, in severe cases, seizures, kidney failure, shock and death

Effects of long-term low intake:

• Higher risk of kidney stones, because urine becomes concentrated [9]

• More frequent urinary tract infections in susceptible people [10]

• Possible links to faster decline in kidney function and to higher risk of high blood sugar [6, 17]

• Observational links between persistently higher serum sodium, a sign of chronic under-hydration, and chronic disease and faster biological ageing [18]. These findings need confirmation from trials.

Who is most at risk. Infants and young children (who lose water quickly through diarrhoea and fever), older adults (blunted thirst), outdoor workers and athletes, pregnant and breastfeeding women, and people with diabetes, kidney disease or gastrointestinal illness.

Warning signs that need urgent medical help: very little or no urine for 8 hours or more, sunken eyes, no tears in a crying child, extreme drowsiness or confusion, a rapid pulse with cold hands and feet, or persistent vomiting that prevents drinking.

Note. This article is for general information and is not personal medical advice. If you have a medical condition or take regular medication, ask your doctor how much you should drink.

:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

Bibliography

[1] World Health Organization. Guidelines for drinking-water quality: fourth edition incorporating the first and second addenda. Geneva: WHO; 2022. ISBN 978-92-4-004506-4. https://www.who.int/publications/i/item/9789240045064

[2] World Health Organization. Guidelines for drinking-water quality: fourth edition incorporating the first, second and third addenda. Geneva: WHO. https://www.who.int/publications/i/item/9789240121225

[3] EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). Scientific Opinion on Dietary Reference Values for water. EFSA Journal. 2010;8(3):1459. https://www.efsa.europa.eu/en/press/news/nda100326

[4] Institute of Medicine, Panel on Dietary Reference Intakes for Electrolytes and Water. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC: National Academies Press; 2005. https://www.nationalacademies.org/news/report-sets-dietary-intake-levels-for-water-salt-and-potassium-to-maintain-health-and-reduce-chronic-disease-risk

[5] Armstrong LE, Johnson EC. Water intake, water balance, and the elusive daily water requirement. Nutrients. 2018;10(12):1928.

[6] Clark WF, Sontrop JM, Macnab JJ, et al. Urine volume and change in estimated GFR in a community-based cohort study. Clin J Am Soc Nephrol. 2011;6(11):2634-2641.

[7] Clark WF, Sontrop JM, Huang SH, et al. Effect of coaching to increase water intake on kidney function decline in adults with chronic kidney disease: the CKD WIT randomized clinical trial. JAMA. 2018;319(18):1870-1879.

[8] Cheuvront SN, Kenefick RW. Dehydration: physiology, assessment, and performance effects. Compr Physiol. 2014;4(1):257-285.

[9] Borghi L, Meschi T, Amato F, et al. Urinary volume, water and recurrences in idiopathic calcium nephrolithiasis: a 5-year randomized prospective study. J Urol. 1996;155(3):839-843.

[10] Hooton TM, Vecchio M, Iroz A, et al. Effect of increased daily water intake in premenopausal women with recurrent urinary tract infections: a randomized clinical trial. JAMA Intern Med. 2018;178(11):1509-1515.

[11] Ganio MS, Armstrong LE, Casa DJ, et al. Mild dehydration impairs cognitive performance and mood of men. Br J Nutr. 2011;106(10):1535-1543.

[12] Armstrong LE, Ganio MS, Casa DJ, et al. Mild dehydration affects mood in healthy young women. J Nutr. 2012;142(2):382-388.

[13] Arnaud MJ. Mild dehydration: a risk factor of constipation? Eur J Clin Nutr. 2003;57(Suppl 2):S88-S95.

[14] Sawka MN, Burke LM, Eichner ER, et al. American College of Sports Medicine position stand: exercise and fluid replacement. Med Sci Sports Exerc. 2007;39(2):377-390.

[15] Spigt M, Weerkamp N, Troost J, van Schayck CP, Knottnerus JA. A randomized trial on the effects of regular water intake in patients with recurrent headaches. Fam Pract. 2012;29(4):370-375.

[16] Dennis EA, Dengo AL, Comber DL, et al. Water consumption increases weight loss during a hypocaloric diet intervention in middle-aged and older adults. Obesity (Silver Spring). 2010;18(2):300-307.

[17] Roussel R, Fezeu L, Bouby N, et al. Low water intake and risk for new-onset hyperglycemia. Diabetes Care. 2011;34(12):2551-2554.

[18] Dmitrieva NI, Gagarin A, Liu D, Wu CO, Boehm M. Middle-age high normal serum sodium as a risk factor for accelerated biological aging, chronic diseases, and premature mortality. eBioMedicine. 2023;87:104404.

[19] Bureau of Indian Standards. IS 10500:2012, Drinking Water: Specification (second revision). New Delhi: BIS.

[20] Hew-Butler T, Rosner MH, Fowkes-Godek S, et al. Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference. Clin J Sport Med. 2015;25(4):303-320.

[21] Lacey J, Corbett J, Forni L, et al. A multidisciplinary consensus on dehydration: definitions, diagnostic methods and clinical implications. Ann Med. 2019;51(3-4):232-251.

Note on sources: the WHO, EFSA and National Academies figures were checked against the organizations' own publications and announcements. Journal citations are given from the published literature; please verify volume and page details against PubMed or the publisher before using them in formal academic work.

MAHINIKA Health And Lifestyle