Pourquoi faut-il boire de l'eau ? Pour maintenir la balance hydrique

How much water we really need depends on the water functions and the mechanisms of daily water balance regulation. The aim of this review is to describe the physiology of water balance and, consequently, to highlight the new recommendations concerning water requirements. Water plays numerous roles in the human body: building material, solvent, reaction medium, reactant, carrier for nutrients and waste products, thermoregulation, lubricant and shock absorber. The regulation of the water balance is very precise since a loss of 1% of body water is usually compensated within 24 hours. Both water intake and water losses are controlled to reach water balance. 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). Water needs are based on experimentally derived intake levels that are expected to meet nutritional adequacy of a healthy population. On average, a sedentary adult should drink 1.5 L of water per day as water is the only liquid nutrient which is really essential for body hydration.