Nothing refreshes like an ice-cold glass of water on a hot summer day. Water replenishes the body's cooling system, enabling it to survive sweltering heat or elevated body temperatures due to exercise. Sweating cools the body by evaporating water on the surface of the skin and dispersing excess heat. But until the tap runs dry, most people take water for granted. Although deficiencies of other nutrients can be sustained for months or even years, a person can survive only a few days without water.
Experts rank water second only to oxygen as essential for life.
In addition to offering true refreshment for 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 in digestion, absorption, circulation and 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 those nutrients can be absorbed in the intestine. Water comprises about 50 to 70 percent of body weight in humans.