Water makes up about sixty percent of the weight of an adult body. It takes part in the work of almost every organ. It carries food to the cells. It helps the body to get rid of waste. It also keeps the body's temperature steady through sweat. When the body loses more water than a person drinks, he may have a headache, feel tired and have a dry mouth. There is no one amount that suits everyone. An athlete in summer needs more water than a person who sits in a cool place. The best sign of enough water is light-colored urine. A person should not wait for thirst before he starts to drink.

Question: In the text, the word "waste" means: