Daily consumption of drinking water

The recommended daily amount of drinking water for humans varies. It depends on activity, age, health, and environment. In the United States, the Adequate Intake for total water, based on median intakes, is 4.0 L per day for males older than 18, and 3.0 L per day for females over 18; it assumes about 80% from drink and 20% from food. The European Food Safety Authority recommends 2.0 L of total water per day for women and 2.5 L per day for men.

The common advice to drink 8 glasses (64 USoz) of plain water per day is not scientific; thirst is a better guide for how much water to drink than is a specific, fixed amount. Americans aged 21 and older, on average, drink 1,043 mL of drinking water a day, and 95% drink less than 2,958 mL [of what?] per day. Exercise and heat exposure cause loss of water and therefore may induce thirst and greater water intake. Active people in hot climates may need 6.0 L of water, or more, per day.

How much drinking water contributes to the intake of mineral nutrients is unclear. Inorganic minerals generally enter surface water and groundwater via stormwater runoff and through the ground. Water treatment also adds some minerals, such as calcium, zinc, manganese, phosphate, fluoride, and sodium compounds. Water generated by the biochemical metabolism of nutrients provides a significant part of the daily water needs for some arthropods and desert animals, but provides only a small fraction of a human's necessary intake. There are trace elements in almost all potable water; some of these affect metabolism, such as sodium, potassium, and chloride, which are common in small amounts in most water. Other elements, such as fluoride, while beneficial in low concentrations, can cause dental and other problems at high levels.

Fluid balance is important to health. Profuse sweating can increase the need to replace electrolytes (salts). Water intoxication (the consumption of too much water too quickly) causes hyponatremia, which can cause death in minutes or hours. Water makes up about 60% of the body weight in men and 55% of weight in women. A baby is about 70% to 80%; old people are about 45% water.