Thirst Water is more essential to the body than food. Without water, a person would die after two or three days. An adult's body is about 60 percent water. Every cell in the body depends on water to carry nutrients and oxygen to the cells and to remove waste from the body.
Water is the body's natural air-conditioning system.
Sweat cools the body and prevents internal heat from getting too high. Thirst lets us know when the body needs more water. Thirst, however, isn't always a good guide for how much to drink. In hot weather or during exercise, a person needs to drink more than his thirst indicates. As people age, they have a reduced sense of thirst.