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. Drink when you are thirsty and glance at the color of your urine, and that is enough. People who work in the heat, do hard exercise, have had kidney stones, or are older and don't feel thirsty much 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 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. Drink when thirsty and check the color of your urine; that is enough. People who work in high heat, who exercise hard, who have had kidney stones, and who don't feel thirsty as they get older should drink on purpose, which is a separate case
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 Content may be out of date and rules differ by place.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