Hydration
How Much Water Should You Drink Per Day?
The science behind the '8 glasses a day' rule and what to do if you sweat a lot.
6 min read·Updated 25 June 2026
HG
HealthGood Editorial Team
Last updated 25 June 2026
Reviewed by HealthGood Editorial Standards Board
There is no single right number of glasses of water per day. Needs vary by body size, activity, climate, and overall diet (food can contribute 20% or more of daily fluid intake).
Sensible starting points
- U.S. National Academies: about 3.7 L total fluid for adult men, 2.7 L for adult women.
- European Food Safety Authority: 2.5 L for men, 2.0 L for women.
- Rule of thumb: 30–35 ml per kg of body weight from drinks.
Adjust for sweat and climate
Add roughly 500–750 ml for every hour of moderate exercise. Hot, humid weather increases needs further.
Frequently asked questions
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References
- World Health Organization — Body mass index (BMI). https://www.who.int
- NHS — Healthy weight and BMI. https://www.nhs.uk
- Centers for Disease Control and Prevention (CDC) — Healthy Weight, Nutrition, and Physical Activity. https://www.cdc.gov
- Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure. Am J Clin Nutr (1990).