Water calculator
Estimate how much to drink each day: the EFSA reference by sex and activity level, allowing for the water in food. Drink more in heat or during hard workouts.
Drinks ≈ 80% of the EFSA intake (2.0 L women · 2.5 L men) + a little on active days
Your details
No weight needed: EFSA sets water by sex, not by kilograms. You need more in hot weather and with hard training.
Calculating…
Results are for reference only and are not medical advice. For individual guidance, consult a doctor or dietitian.
Next step
Turn the number into a result
This calculation is a guide. In the RESET app it becomes a personal plan that counts calories and macros for you, and opens the transformation programs.
How this calculator works
Briefly and honestly: the science behind it, how far you can trust it, and its limits.
How it works
EFSA sets an adequate intake of total water — drinks and food together: 2.0 L a day for women and 2.5 L for men. About 20% of that usually comes from food, so the calculator shows drinks — about 80% of the intake — and adds a little for sweat at the two most active levels. For “other / prefer not to say” it uses the midpoint, 2.25 L.
Drinks ≈ 80% of the EFSA intake (2.0 L women · 2.5 L men) + a little on active days
What it’s based on
The basis is EFSA’s scientific opinion on dietary reference values for water (2010): an adequate intake of total water for adults of 2.0 L a day for women and 2.5 L for men, at moderate temperature and activity. The value is set by sex, not by kilograms, so the calculator does not ask your weight. The drinks share (~80%) is our arithmetic from the 20–30% of water that usually comes with food. The extra for active days (+0.25 L and +0.5 L) is a cautious convention with no primary source for those exact numbers.
✓
Is it validated?
An adequate intake is the amount that covers practically all healthy adults in ordinary conditions — neither a minimum nor a “more is better” target. The “35 ml per kilogram” rule this calculator used before has no primary source, which is why we dropped it.
Can you rely on it?
Follow your body’s signals: thirst and urine colour. Needs rise in heat, with training, illness, pregnancy and breastfeeding — then drink more than the reference. If a doctor has limited your fluids, follow their advice, not a calculator.
Results are for reference only and are not medical advice. For individual guidance, consult a doctor or dietitian.
For the curious
Deeper: why it works this way, what it does for your body, and what happens if you get it wrong.
Water is involved in almost everything: transporting nutrients, regulating temperature, lubricating joints and keeping you focused. An adult body is 50–60% water, and we constantly lose it — through breathing, sweat and urine.
Some of our water comes with food — vegetables, fruit, soups — so fewer drinks are needed than the total intake. That is why the calculator shows drinks rather than total water: the number is easy to check against the glasses in a day.
Even 1–2% dehydration lowers focus and endurance and often masquerades as hunger. Forcing fluids isn’t necessary either — the most reliable signals come from your body: follow thirst and a light urine colour.
Worked examples
Concrete numbers for common situations — so you can see at a glance how to read the result.
Woman, an ordinary day
- Inputs
- EFSA: 2.0 L of total water · moderate activity
- Result
- ≈ 1.6 L of drinks a day (≈ 6 glasses)
Food brings the rest: soups, vegetables, fruit.
Man, an ordinary day
- Inputs
- EFSA: 2.5 L of total water · moderate activity
- Result
- ≈ 2.0 L of drinks a day (≈ 8 glasses)
Tea and coffee count too; water is the best choice without sugar.
Man, a very active day
- Inputs
- EFSA: 2.5 L · very high activity
- Result
- ≈ 2.5 L of drinks a day (≈ 10 glasses)
About 0.5 L for sweat is added to the usual 2.0 L; heat or a long session may need more — let thirst guide you.
FAQ
Frequently asked questions
How much water should I drink per day?
According to EFSA, about 2.0 L of total water a day is adequate for a healthy adult woman and 2.5 L for a man, including the water in food. Drinks usually make up about 80% of that; heat and training need more.
Why doesn’t the calculator ask my weight?
Because EFSA sets water by sex, not by kilograms. The “35 ml per kilogram” rule has no primary source and overstates the figure at high body weights — so we no longer use it.
Do tea and coffee count?
Yes. Moderate tea and coffee add to your overall fluid balance. Plain water is still the best choice without extra sugar or calories.
How do I know I’m drinking enough?
Watch your body’s signals: no strong thirst and a pale-yellow urine colour usually mean you’re well hydrated. A dark colour is a cue to drink more.
Can I drink too much water?
In extreme cases yes — a very large volume in a short time can disrupt electrolyte balance. For most people this isn’t a concern: drink to thirst, not by force.
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