Eight Glasses of Water Was Never a Finding

Total water intake includes food and other drinks, and thirst is a better regulator than a target.

The eight-glasses figure has no traceable research origin. Reference intakes describe total water from all sources, including food, coffee, and tea, which together cover a large share.

Thirst is a well-calibrated signal in healthy adults under ordinary conditions. It becomes less reliable in older adults, during illness, and in heat or at altitude.

Urine colour is a rough guide with obvious confounders, including B vitamins and some medications. Very pale urine all day usually means drinking beyond need.

Overdrinking is not harmless. Endurance events have produced dangerous hyponatraemia in participants who drank to a schedule rather than to thirst.

Editorial note: this article summarises published research for general information. It is not medical advice. Discuss any intervention with a qualified clinician.