To hear audio pronunciation of this topic, purchase a subscription or log in.

H2O, hydrogen combined with oxygen, forming a clear, tasteless, odorless fluid.
CAS # 7732-18-5

Water freezes at 32°F (0°C) and boils at 212°F (100°C). It is the principal chemical constituent of the body, composing approx. 65% of the body weight of an adult male and 55% of the adult female. It is distributed within the intracellular fluid and outside the cells in the extracellular fluid. Water is indispensable for metabolic activities within cells, being the medium in which chemical reactions usually take place. Outside of cells, it is the principal transporting agent of the body. The following properties of water are important to living organisms: it is an almost universal solvent; it is a medium in which acids, bases, and salts ionize, and the concentrations of these substances (electrolytes) are regulated by the body; it possesses a high specific heat and has a high latent heat of vaporization (important in regulating a constant body temperature); it possesses a high surface tension; and it is an important reacting agent and essential in all hydrolytic reactions.

Water is the principal constituent of all body fluids (blood, lymph, tissue fluid), secretions (saliva, gastric juice, bile, sweat), and excretory fluid (urine). Intake of water is determined principally by the sense of thirst. Excessive intake may lead to water intoxication; excessive loss to dehydration. Humans can survive for only a short time without water intake. The exact length of survival time varies with ambient temperature, moisture in available food, and amount of physical activity.

There's more to see -- the rest of this topic is available only to subscribers.