How it works
- Start from about 30 millilitres per kilogram of body weight.
- Add 500 millilitres for an active day and a litre for hard training.
- The glass count divides the target by a 250-millilitre glass.
Good to know
- Food and all drinks add water, but alcohol drains more than it gives.
- Heat, fever, breastfeeding and long workouts raise needs well above the estimate.
- Nothing is stored or sent anywhere.
Standards and sources
Last reviewed October 10, 2026
Frequently asked questions
How is it calculated?
About 30 millilitres per kilogram of body weight, plus 500 millilitres for an active day and 1 litre for hard training.
Does coffee count?
Partly. Food and all drinks add water, but alcohol drains more than it gives; use plain water for the target.
When do I need more?
Heat, fever, vomiting, diarrhoea, breastfeeding and long workouts all raise needs well above the estimate.