ABSTRACT
Water is essential to life, and body water content is normally tightly regulated and remains relatively constant from day to day. Water losses are increased by increasing ambient temperature and humidity, and by increasing levels of physical activity. A variety of foods and beverages normally contribute to total daily water intake. The ability to regulate body water content and the osmolality of tissues within a relatively narrow range is one of the defining characteristics of all animal life. Physical activity poses a number of challenges to water and salt homeostasis, including increased rates of water and salt loss. Water balance occurs when water intake matches water losses, but water intake is episodic whereas water losses are continuous, so water balance fluctuates throughout the course of a day. Much attention has been given to the acute and chronic effects of hypohydration, but large, acute increases in body water, though less common than hypohydration, can also be hazardous.
