Perspiration or sweating is the body's way to deal with the heat generated from exercise or heat in the environment. As water evaporates on the surface of the skin , heat is lost to the environment. Body water is routinely lost via perspiration and by the humidification of the air that enters and leaves the lungs. Some water is lost in the voiding of wastes via the urine and feces as well. Hot, dry climates, exercise, and fever increase water losses from the skin and lungs.
Humid environments decrease the degree to which sweat vaporizes.
In a dry environnment, most of the sweat produced, even in extreme exercise, evaporates into the air. Diarrhea can result in very large water losses. Water must be replaced to maintain fluid balance. No minimum daily requirement for water has been established, although a general guideline is set at eight glasses of water per day. People who engage in strenuous exercise or work outside in hot climates, have a fever, vomiting, diarrhea , or excessive urine losses , those on high protein diets or taking diuretics have increased fluid needs.