How much water you need a day, from official guidance for your age and sex, plus exercise and hot weather.
Total water from drinks and food. Food such as fruit, vegetables, dal and rice supplies part of it, so the amount you drink is a bit less.
Covers the full amount. If you eat plenty of fruit, vegetables, soup or dal, a little less from drinks is fine.
8 glasses of 250 ml, about one every 2.1 hours.
A general guide for healthy people. If you have kidney, heart or liver disease, or your doctor has set a fluid limit, follow their advice instead.
This is a general estimate based on standard published formulas, not a medical assessment — it doesn’t account for your individual health history. Results are informational only and aren’t a substitute for advice from a doctor or qualified professional. Read the full disclaimer.
Many water calculators multiply your weight by a fixed number, which gives heavier people targets far above what health authorities recommend. This one starts from the European Food Safety Authority's adequate intakes for your age, sex, pregnancy or breastfeeding, then adds what exercise and hot weather take out through sweat. You get a daily target and a simple glass-by-glass plan for your waking hours.
EFSA's adequate intake is 2.0 litres of total water a day for women and 2.5 litres for men, counting both drinks and food. Add more on hot days and when you exercise. The calculator adds these for you.
It's close for many adults: eight 250 ml glasses is 2 litres. But part of your water comes from food, and needs rise with heat and exercise, so there isn't one number for everyone.
Official reference values are set by age and sex, not weight. The 30–35 ml per kg rule of thumb is shown for comparison only; for heavier people it can give much higher numbers than needed.
A common starting point is 0.4 to 0.8 litres per hour of exercise, more in heat or if you sweat heavily. Weighing yourself before and after a session shows your own sweat loss: each kilogram lost is about a litre of fluid.
Yes. EFSA's figures include beverages of all kinds as well as water in food. Caffeine in normal amounts doesn't cancel out the water in the drink.
Yes. Drinking much more than about a litre an hour, for example during long endurance events, can lower blood sodium (hyponatraemia). Spread drinks through the day and, on long sweaty sessions, have some salt too.
No. It's a general guide for healthy people. Children's needs, illness, fever and medications can change requirements, so ask a doctor when in doubt.
