Water is the second essential need of the human body to that of oxygen. One can live without food for days, but cannot live without water for a few hours. Nearly 70 percent of the total body weight is composed of water.
1. Water is a universal solvent and is able to dissolve all the products of digestion.
2. Because nutrients and cellular wastes are soluble in water. It is the means by which nutrients are carried to the cells and wastes are removed from the lungs, kidneys, gut and skin.
3. Water is the structural component and a cushion of all cells. Thereby it prevents friction between moving parts of the body.
4. Water regulates the body temperature through evaporation of water from the skin and lungs.
5. Water acts as a body lubricant: The saliva making swallowing possible, the mucous secretion of the gastrointestinal tract makes food pass through it, in respirations and genitourinary tracts and so on.
6. Water is the medium of all body fluids including the digestive juices, the lymph, the blood, the urine and the perspiration. All the physiochemical changes that occur in the cells takes place in the regulated environment of the body fluids.
Water is supplied to the body through (1) the ingestion of water and beverages (2) the performed water in foods and (3) the water resulting from the oxidation of food stuffs.
The amount of water needed by an individual depends upon atmospheric temperature, humidity, occupation and the diet. On an average, a man needs 1.5 to 2 liters of drinking water daily.
Normally, the body maintains a good water balance, in spite of varied intake of water from day to day. However loss of water occurring due to diarrhea and vomiting may cause dehydration and sometimes be fatal. Even during excessive perspiration due to extreme exercise may result in heavy loss of water from the body. In all such cases, the body has to replace the water and soluble salts lost to maintain body composition.
Progressive deficiency of water may cause poor absorption of food, delayed elimination of wastes, elevation of body temperature, failure of the circulatory system and even malfunctioning of the renal system may occur.