Following a request from the European Commission, the EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA) was asked to deliver a scientific Opinion on Population Reference Intakes.
Water is consumed from different sources, which include drinking water (tap and bottled water), beverages, moisture content of foods, and water produced by oxidative processes in the body. Water intake from beverages and foods is defined as total water intake, while the sum of total water intake and oxidation water constitutes total available water.
Water is essential for practically all functions of the body and is particularly important for thermoregulation.
A water intake which balances losses and thereby assures adequate hydration of body tissues is essential for health and life.
The water content of the body and the distribution of body water over the intracellular and extracellular compartments of the body changes with age, but is under tight homeostatic control for an individual in a given stage of life.
Loss of body weight, denoting loss of body water, of about 1% is normally compensated within 24 hours. Without compensation and further increases of losses of body water, reductions in physical and cognitive performance, in thermoregulation and cardiovascular function occur. A loss of 10% or more of body water can be fatal.
Water intoxication with life-threatening hypo-osmolarity is rare but can occur in rapid rehydration, with near-drowning in fresh water and in overconsumption of water, which exceeds the kidney’s maximal excretion rate of 0.7-1.0 L/hour.
Water requirement varies between individuals and according to environmental conditions. Therefore, only adequate intakes have been defined for specific age groups from a combination of observed intakes in population groups with desirable osmolarity values of urine and desirable water volumes per energy unit consumed.
The Panel has decided that the reference values for total water intake should include water from drinking water, beverages of all kind, and from food moisture.
The Panel concludes that on the basis of available data, adequate intakes can be defined for infants in the first half of the first year of life based on water intake from human milk in exclusively breast-fed infants (100-190 mL/kg per day).
For older infants adequate intakes can be derived from observed intakes of human milk and typical patterns of complementary food and beverages. The Panel concludes that a total water intake of 800 to1000 mL/day is adequate for the age period 6 to 12 months. For the second year of life an adequate total water intake of 1,100 to 1,200 mL/day is defined by interpolation, as intake data are not available.
The Panel concludes that adequate intakes of water for children can be derived from observed intakes, corrected for a desirable water-energy relationship and corrected for inter-individual variation, particularly from those studies in which the water contribution by food has been or can be assessed (see section 3): 1,300 mL/day for boys and girls 2 to 3 years of age; 1,600 mL/day for boys and girls 4 to 8 years of age; 2,100 mL/day for boys 9 to 13 years of age; 1,900 mL for girls 9 to 13 years of age. Adolescents of 14 years and older are considered as adults with respect to adequate water intake and the adult values apply.
The Panel concludes that available data for adults permit the definition of adequate intakes and that these adequate intakes should be based both on observed intakes and on considerations of achievable or desirable urine osmolarity. Adequate total water intakes for females would have to be 2.0 L/day (P 95 3.1 L) and for males 2.5 L/day (P95 4.0 L). The Panel defines the same adequate intakes for the elderly as for adults. Despite a lower energy requirement, the water requirement in the elderly per unit of dietary energy becomes higher because of a decrease in renal concentrating capacity.
The Panel did not find data on habitual water intake in pregnant women and proposes the same water intake as in non-pregnant women plus an increase in proportion to the increase in energy intake (300 mL/day).
The Panel recommends adequate water intakes for lactating women of about 700 mL/day above the adequate intakes of non-lactating women of the same age.
These adequate intakes apply only to conditions of moderate environmental temperature and moderate physical activity levels (PAL 1.6). Water losses incurred under extreme conditions of external temperature and physical exercise, which can be up to about 8,000 mL/day have to be replaced with appropriate amounts. In such instances concomitant losses of electrolytes have to be replaced adequately to avoid hypo-osmolar disturbances.
Too high intakes of water which can not be compensated by the excretion of very dilute urine (maximum urine volumes of about one litre/hour in adults) can lead to hyponatraemic, hypo-osmolar water intoxication with cerebral oedema. 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.