Water is the largest constituent in the body. The body's need for body is second only th that for oxygen. One can live for weeks without food, but death is likely to follow a deprivation of water for more than a few days. Water is essential as body lubricant: the saliva that makes possible the swallowing of food, the fluid that bathe the joints and so on. Sources of water to the body are : ingestion of water and beverages, the preformed water in foods and the water resulting from oxidation of food stuffs. The 24-hour water requirement is that amount of water replaces the losses by kidneys, lungs, skin, and the bowel. Ordinarily, thirst is an accurate guide to supplying the necessary amounts of water. Under ideal conditions including a low-solute diet, a minimum of physical activity, and the absence of sweating, the water need for adult is about 1.5 litres from beverages, food and water of oxidation.Although conditions are variable, the daily requirement is about 1ml per kcal for adults and 1.5ml per kcal for infants.