Don’t force yourself to drink water just to hit “8 glasses a day”

Someone chased down the source of “8 glasses a day” and found not a single study that supports it. Food and other drinks already carry a lot of water, so you need not drink that much. This conclusion applies only to healthy adults who live in a mild climate and are not very active. Hot outdoor work, hard exercise, and people who must drink more for treatment or prevention should drink more on purpose.

Cost

No money. It takes a little time and attention to remember to drink, and night trips to the toilet also increase.

Benefit

One literature review specifically checked the “8×8” claim — 8 glasses a day, 8 ounces each. Its conclusion was “no scientific study supporting 8×8 was found.” It also wrote that “surveys of food and fluid intake in thousands of adults strongly suggest such a large amount is not needed,” because food and other drinks already supply a lot of water. The author states clearly that this conclusion applies only to “healthy adults in a temperate climate who sit most of the time.” He also wrote that some treatments or prevention need 8×8 or more, and that “hard labor and exercise, especially in hot climates,” of course need more. The claim looks worthwhile because water is free, 8 is a neat number, and “drink more water” sounds harmless in any setting.

Notes

What to reject is the number “you must drink so many glasses a day,” not the idea that drinking more water is harmful. People working in heat and people doing hard exercise are a separate case and should drink on purpose. People who have had kidney stones should drink more — see Section 16, Item 8 (after kidney stones, get the water up). The next two lines are common-sense reminders; the review in the sources line does not state them: drink when thirsty and check urine color; older people who feel thirst less should drink on purpose.

Sources · 1

1. Valtin H (2002). "Drink at least eight glasses of water a day." Really? Is there scientific evidence for "8 x 8"? Am J Physiol Regul Integr Comp Physiol. doi.org/10.1152/ajpregu.00365.2002