Do not force yourself to reach “eight glasses of water a day”
A review tracing the origin of “eight glasses a day” found no scientific study supporting that exact rule. Food and other drinks already supply a substantial amount of water. For most people, thirst and urine color are useful guides. Working in heat, vigorous exercise, a history of kidney stones, and reduced thirst in older age call for more deliberate attention to drinking.
What it takes
Water itself costs little or nothing, but remembering to drink takes time and attention, and may mean more trips to the bathroom at night.
What you may gain
A literature review investigated the “8×8” rule: eight 8-ounce glasses of water each day. It found no scientific studies supporting that requirement. Surveys of food and fluid intake in thousands of adults also strongly suggested that such a large additional amount was unnecessary, because food and other beverages already supply considerable water. The advice sounds appealing because water is inexpensive, eight is an easy number to remember, and “drink more water” sounds harmless in almost any setting.
Context & considerations
The target here is a mandatory number of glasses, not a claim that drinking water is harmful. Thirst and urine color are usually enough to guide ordinary drinking. People working in high temperatures, exercising vigorously, or living with a history of kidney stones, and older people whose thirst response is weaker, need to drink more proactively.
Research & references
Valtin H (2002). “Drink at least eight glasses of water a day.” Really? Is there scientific evidence for “8 x 8”? American Journal of Physiology—Regulatory, Integrative and Comparative Physiology. https://doi.org/10.1152/ajpregu.00365.2002.