The average human exhales 0.35 liters of water each day. Additional water loss occurs through urine, bowel movements and perspiration. The total fluid lost from these processes is about 2.5 liters daily.
Water is necessary for human life. The average person can go for less than a week without water. Daily water requirements vary depending upon level of physical activity, health and climate as well as during pregnancy or while breastfeeding. Those engaging in exercise or living in hotter climates require more water because they lose more than average through perspiration. Illness can also cause a person to lose additional fluids through fever, vomiting or diarrhea.