Hydration: How Much Water Do You Need?
The eight-glasses rule is a rounding error dressed as science. Needs vary — here is what shapes them.
Nutritional Density editorial team12 January 20265 min read
Last reviewed
Fluid needs are shaped by body size, activity, climate, and diet. A fixed number is convenient and usually wrong.
Reference intakes
EFSA sets adequate intakes of roughly 2.0 litres per day for women and 2.5 litres for men, from all drinks and food combined. Water-rich foods — fruit, vegetables, soups, yogurt — typically supply a fifth to a third of the total.
What counts
Almost everything you drink contributes. Moderate caffeine intake has a mild diuretic effect that does not offset the fluid in the drink itself. Alcohol is the exception worth noting, as it increases fluid loss.
Exercise and electrolytes
For most sessions under an hour, water is sufficient. Longer or hot sessions with heavy sweating increase sodium losses, where an electrolyte drink or salted food afterwards is reasonable. Drinking very large volumes of plain water in a short period is not harmless.
Sources
- Dietary reference values for water — EFSA
- Healthy diet fact sheet — World Health Organization
Where a claim could not be confidently supported by a credible source, it has been qualified or left out. Read our sources policy.
Educational content. This article is for general information and is not medical advice. Speak to a qualified health professional about your individual circumstances.
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