5 Feb 2010 --- Water is a vital nutrient. We can't live without it. But how much do you need?  In a review just published in The European Journal of Clinical Nutrition, Professor Eric Jéquier and Dr Florence Constant, Nestlé Waters, conclude that people should drink about 1.5 litres per day.

This estimate is based on a thorough understanding of water requirements by individuals at different stages of the life cycle and under different environmental and physiological situations. There are some differences in the recommendations for Europe compared with the USA, which reflect differences in dietary patterns between Europe and the USA. However, there is general agreement that adults are less at risk of dehydration than infants and the elderly.

Water has numerous roles in the human body, the paper notes. It acts as a building material; as a solvent, reaction medium and reactant; as a carrier for nutrients and waste products; in thermoregulation; and as a lubricant and shock absorber. The regulation of water balance is very precise, as a loss of 1% of body water is usually compensated within 24|[thinsp]|h. Both water intake and water losses are controlled to reach water balance. Minute changes in plasma osmolarity are the main factors that trigger these homeostatic mechanisms.

Healthy adults regulate water balance with precision, but young infants and elderly people are at greater risk of dehydration. Dehydration can affect consciousness and can induce speech incoherence, extremity weakness, hypotonia of ocular globes, orthostatic hypotension and tachycardia. Human water requirements are not based on a minimal intake because it might lead to a water deficit due to numerous factors that modify water needs (climate, physical activity, diet and so on).

Water needs are based on experimentally derived intake levels that are expected to meet the nutritional adequacy of a healthy population. The regulation of water balance is essential for the maintenance of health and life. On an average, a sedentary adult should drink 1.5|[thinsp]|l of water per day, as water is the only liquid nutrient that is really essential for body hydration.

European Journal of Clinical Nutrition (2010) 64, 115–123; doi:10.1038/ejcn.2009.111; published online 2 September 2009