In Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate, the Institute of Medicine says that an adequate intake for an average adult male is 3.7 liters of total water per day and for an average adult female it is 2.7 liters of total water per day. Under normal conditions, people get adequate hydration by consuming beverages at meals and letting their thirst guide them, However, prolonged physical activity and heat exposure will increase water losses and therefore may raise daily fluid needs. Very active individuals who are continually exposed to hot weather often have daily total water needs of 6 liters or more, according to several studies.

The report notes that hydration needs can be met through a variety of fluids. In addition, people get about 20 percent of their fluids from fruits, vegetables, and other foods they consume.