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

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

Cost: No cost at all. It does require some time and effort to remember to drink, and you’ll likely need to get up more often at night to pee.

In plain terms: Some people have tried to trace the origin of the “8 glasses a day” rule, but no studies supporting it have ever been found. On the contrary, surveys of thousands of adults’ diets and fluid intake show there’s no need for that much water at all, since food and other drinks already provide plenty. Just drink when you’re thirsty, and use the color of your urine as a guide — that’s all you need to do. People working in hot environments, those doing intense exercise, people who’ve had kidney stones, and older adults who no longer feel thirsty as readily should make a conscious effort to drink more water.

Benefit: One literature review specifically examined the “8×8” rule — that is, 8 glasses a day, each glass holding 8 ounces of water. Its conclusion was that “no scientific research supporting the 8×8 guideline has been identified.” It also noted that “surveys of thousands of adults’ food and fluid intake strongly indicate there is no need for such a large volume of water intake,” since food and other drinks already supply plenty of moisture. This idea seems appealing because water costs nothing, the number 8 is easy to remember, and saying “drink more water” never seems like a bad piece of advice in any context.

Evidence grade: C

Sources: 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. <https://doi.org/10.1152/ajpregu.00365.2002>

Notes: This recommendation refutes the idea that there’s a strict minimum number of glasses of water you must drink each day — it does not say that drinking more water is harmful. Just drink when you’re thirsty and check your urine color; that’s sufficient. People working in hot conditions, those doing heavy exercise, people with a history of kidney stones, and older adults who no longer feel thirst as keenly should make a point to drink more water, even though this guideline does not apply to them.