Nothing refreshes like an ice-cold glass of water on a hot day or after an exercise session. Water replenishes the body's cooling system, enabling it to survive sweltering heat or elevated body temperature due to exercise. Sweating cools the body by evaporating water on the surface of the skin and dispersing excess heat. Although deficiencies of other nutrients can be sustained for months or even years, a person can survive only a few days without water.
Water ranks second only to oxygen as essential for life.
In addition to giving refreshment to the thirsty, water plays a vital role in all bodily processes. It supplies the universal medium in which various chemical changes of the body occur, aiding digestion, absorption, circulation and the lubrication of body joints. For example, as a major component of blood, water helps deliver nutrients to body cells and removes waste to the kidneys for excretion. Secretions essential to digestion are also primarily water, working to break down food so that nutrients can be absorbed in the intestine. Males on average have a much higher percentage of body water than females, because they tend to have less body fat.