Hydration levels

Water needs vary between individuals and according to diet, environmental conditions, activity levels and a range of other factors.

Hydration needs

Water is lost from the body predominantly via the kidney as urine and via the skin as sweat. These losses vary widely with the amount of fluid intake, diet, activity level,hydration needs, Hydration levels temperature and clothing. Water balance is achieved when losses are compensated by intake from food and beverages plus metabolic water production.

Water balance normally varies over the course of the day, but is usually regulated to within about 0.2% of the body weight over 24 hours despite the wide variability of food and fluid intake and of water output. Water deficits and excesses trigger compensatory changes in either drinking behaviour or in urine output until water balance is re-established.

Water requirements vary between individuals and according to diet, environmental conditions, activity levels and a range of other factors. Therefore, only adequate intakes can be defined for specific age groups.

The Panel on Dietetic Products, Nutrition and Allergies from the European Food Safety Authority (EFSA)* has issued a Scientific Opinion on Dietary Reference Values for water where the following reference values for total water intake are considered (see table). Note that the amount of water that is deemed adequate includes water from drinking water, beverages of all kind, and from food moisture and only apply to conditions of moderate environmental temperature and moderate physical activity levels.

* EFSA Panel on Dietetic Products, Nutrition, and Allergies (NDA); Scientific Opinion on Dietary reference values for water. EFSA Journal 2010; 8(3):1459. [48 pp.]. doi:10.2903/j.efsa.2010.1459. Available online:www.efsa.europa.eu.

Reference values for total water intake

Age range

Daily adequate water intake

Infants
0-6 months 680 mL/day or 100-190 mL/kg/day. From human milk
6-12 months 0.8-1.0 L/day. From human milk and complementary foods and beverages
1-2 years 1.1-1.2 L/day
Children
2-3 years 1.3 L/day
4-8 years 1.6 L/day
Adolescents
9-13 years – Males 2.1 L/day
9-13 years – Females 1.9 L/day
14-18 years – Males 2.5 L/day
14-18 years – Females 2.0 L/day
Adults
19-70 years – Males 2.5 L/day
19-70 years – Females 2.0 L/day
Special cases
Pregnant women 2.3 L/day
Lactating women 2.7 L/day
Adapted from: EFSA Panel on Dietetic Products, Nutrition, and Allergies (NDA); Scientific Opinion on Dietary reference values for water. EFSA Journal 2010; 8(3):1459. [48 pp.]. doi:10.2903/j.efsa.2010.1459. Available online:www.efsa.europa.eu

Water losses under extreme conditions of external temperature and physical exercise can be up to about 10-12 L/day or even more. These high losses have to be replaced adequately to avoid serious disturbances of water and salt balance.

In cases of severe diarrhoea, water losses can also be very high. Cholera is fortunately rare, but it can lead to severe diarrhoea with up to half of the total body water being lost by this route in a single day. Treatment involves drinking plenty of fluids, especially oral rehydration solutions that can be obtained from a pharmacy. These will replace some of the salts that are being lost along with the water. Isotonic sports drinks may be used if oral rehydration solutions are not readily available.

Intakes of water that are too high cannot be compensated by the excretion of very dilute urine (maximum urine volumes are about 1 L/hour in adults) and can lead to water intoxication, possibly leading to swelling of the brain. This is a serious condition, with occasionally fatal consequences. No maximum daily amount of water that can be tolerated by a population group can be defined without taking into account individual and environmental factors.

Please see our downloadable educational tool about this specific topic

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