Everyone needs eight glasses of water a day
Hydration matters, but the specific 8×8 rule has no clear evidential origin. Needs vary with body size, climate and activity, and food contributes a fifth of intake.
AI review of the sources below, no human approval · Reviewed
This verdict was generated by AI from the papers listed on this page and published without human sign-off. AI can misread or miss studies — check the sources yourself. Not medical advice.
What the research says
A review in the American Journal of Physiology traced the '8 glasses a day' rule and found no scientific basis for it as a universal target. Health authorities set adequate-intake figures for total water — around 2.0 L/day for women and 2.5 L/day for men in temperate climates — that explicitly include water from food and all beverages, not eight glasses of plain water on top of a normal diet.
Caveats
- Requirements rise substantially with heat, illness and physical exertion.
- Some conditions (heart failure, kidney disease) require restricted intake — follow clinical advice.
Evidence
- Systematic reviewAmerican Journal of Physiology·2002
Drink at least eight glasses of water a day. Really?
No scientific evidence found supporting the 8×8 rule as a universal requirement.
Read the source - GuidelineEuropean Food Safety Authority·2010
Scientific opinion on dietary reference values for water
Adequate total water intake: 2.0 L/day (women), 2.5 L/day (men), including water from food.
Read the source
More in Nutrition
Sugar makes children hyperactive
Double-blind trials find no effect of sugar on children's behaviour. Parental expectation explains most of the reported effect.
Detox diets and cleanses remove toxins from the body
No commercial detox regimen has been shown to eliminate any named toxin. The liver and kidneys already do this job.
This page summarises published research for general information. It is not medical advice — talk to a clinician about your own situation.