[How much water do we really need to drink?]

Abstract

Everywhere around us we see people sipping bottled water. In healthy people, the fluid balance is strictly regulated via osmoregulation by the hormone vasopressin and the kidneys, in combination with the thirst mechanism and drinking. Fluid intake comes from food, metabolism and beverages, including water. People lose fluid via the skin, respiration, faecal fluid and urinary output. The obligatory urine volume is determined by maximal renal concentrating ability and the solute load which must be excreted. Under normal circumstances of diet, exercise and climate the minimal urine output for healthy subjects is about 500 ml/day. Intake of more than 500 ml of fluids per day will result in the excretion of solute-free water. The recommended total daily fluid intake of 3,000 ml for men and of 2,200 ml for women is more than adequate. Higher fluid intake does not have any convincing health benefits, except perhaps in preventing (recurrent) kidney stones.