Don't force yourself to drink to reach “8 glasses a day”

Moderate value
Evidence C
Saves money
Free
Takes minutes
No willpower

In plain words

Someone went looking specifically for where “8 glasses a day” came from and could not find a single study that supports it. Food and other drinks already carry a lot of water, so you do not need to drink that much. This conclusion applies only to healthy adults who live in a mild climate and mostly sit. People who work in the heat, exercise hard, or need to drink more to treat or prevent a disease should drink on purpose.

Cost: Free. It costs a little time and effort to remember to drink, and you will get up more at night.
What you get: A literature review looked specifically at the “8×8” claim, meaning 8 glasses a day, 8 ounces each. Its conclusion was “no scientific studies were found to support 8×8.” It also wrote that “surveys of food and fluid intake in thousands of adults strongly suggest that such large amounts are not needed,” because food and other drinks already provide a lot of water. The author specifically wrote that this conclusion applies only to “healthy adults in a temperate climate who are mostly sedentary.” He also wrote that treating or preventing some illnesses calls for drinking 8×8 or more, and that “strenuous labor and exercise, especially in hot climates,” naturally calls for drinking more. The claim looks like a good deal because water is free, the number 8 is tidy, and “drink more water” sounds harmless in any setting
Notes: What is being ruled out is the number “you must drink this many glasses a day,” not the idea that drinking more water is harmful. People who work in high heat or exercise hard are a separate case and should drink on purpose. If you have had kidney stones, drink more; see §16.8 (if you have had kidney stones, drink enough water to reach the target). The next two sentences are common-sense reminders that the paper in the sources column does not state: drink when you are thirsty and check the color of your urine; people who don't feel thirsty much as they get older should drink on purpose
Evidence grade: C : The author's experience or common practice, without direct literature.
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

Translated from the Chinese original. Original book, section 6, tip 14. Content may be out of date and rules differ by place. When you actually deal with an agency, a doctor or a court, follow what local officials, doctors and lawyers tell you. Disclaimer