According to the Institute of Medicine, an adequate intake of water for men is about 13 cups per day. For women, an adequate intake is 9 cups per day. These figures are based on average healthy adults who live in a mild climate.
The Centers for Disease Control and Prevention reports that, although there are recommended daily amounts for water intake, more water is necessary in certain conditions. People living in hotter climates, who are physically active, or who are sick with a fever or diarrhea require more water to replenish bodily fluids and prevent dehydration.
Water accounts for about 60 percent of a person's body weight and is involved in every bodily function, according to the Mayo Clinic. It flushes toxins out of organs, provides a moist environment for soft tissues such as the nose and throat, and transports nutrients between cells.