Water intake calculator
Water intake calculator: how much water you need a day
Official guidance puts total water at about 2.0 litres a day for women and 2.5 litres for men (EFSA), counting drinks and the water in food. Add your exercise and sweat rate to see how much more to drink.
Your daily water
For healthy adults. If a doctor has given you a fluid limit, follow that instead.
Example: a woman, EFSA, 45 minutes of exercise at a measured 0.8 L an hour
Total water a day
2.6 L
From drinks (about)
1.6 L
Extra for exercise
0.6 L
Where the numbers come from
| EFSA (Europe) | US National Academies | |
|---|---|---|
| Women | 2 L | 2.7 L |
| Men | 2.5 L | 3.7 L |
| Pregnancy | 2.3 L | 3 L |
| Breastfeeding | 2.7 L | 3.8 L |
Both bodies set an adequate intake: the amount healthy people typically take in, judged to be enough, rather than a measured minimum. The US figures are higher because they were based on what Americans actually consume. In US surveys food supplied about 19% of total water, so the amount to drink is lower than the headline figure: the National Academies put it at about 2.2 litres for women and 3.0 for men.
The “8 glasses” rule
Eight 250 ml glasses is 2 litres, close to EFSA’s figure for women from drinks and food together. But there is no study behind “8 glasses of water on top of everything else”: tea, coffee, milk and the water in food all count. Thirst is a reasonable guide for most healthy adults day to day.
Exercise and heat
Sweat losses vary widely with effort, heat and the person, so this calculator doesn’t guess yours. The American College of Sports Medicine suggests drinking enough to avoid losing more than about 2% of body weight during exercise, without drinking so much that you gain weight. Weighing yourself before and after a typical session shows your own losses: each kilogram lost is about a litre, plus whatever you drank during the session. Divide by the hours to get the sweat rate the calculator asks for.
When to follow your doctor instead
People with heart failure, kidney disease or some other conditions may be told to limit fluids. Some medicines change how the body handles water and salt. In those cases a doctor’s advice comes first. Drinking very large amounts quickly can also be harmful, especially during long endurance events.
Water in Bodyvault
Log water with one tap on the iPhone, Apple Watch or a Control Center button, and Bodyvault can nudge you when you are behind your usual pace for the day. For more daily estimates, see the calorie deficit calculator and the protein calculator.
Privacy
The calculation runs in this page. Nothing you type is sent to a server, saved in your browser or put into the address bar; reloading the page restores the example. The site’s usual behaviour is in the privacy policy.
Questions
How much water should I drink a day?
EFSA’s adequate intake of total water is 2.0 L for women and 2.5 L for men, counting the water in food, which supplied about a fifth of total water in US surveys. That leaves roughly 1.6 L (women) and 2.0 L (men) from drinks, plus more when you sweat.
Do tea and coffee count?
Yes. All drinks count toward total water, including tea, coffee and milk.
How much more should I drink when I exercise?
It depends on how much you sweat, which varies a lot with effort, heat and the person. Weigh yourself before and after a session: each kilogram lost is about a litre to replace. The ACSM suggests avoiding losses of more than about 2% of body weight.
Is my data saved?
No. The calculation runs in the page and nothing is sent anywhere.
Sources
- EFSA Panel on Dietetic Products, Nutrition and Allergies (2010). Scientific opinion on dietary reference values for water. EFSA Journal 8(3):1459.
- National Academies (2005). Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate.
- Sawka MN et al. (2007). ACSM position stand: exercise and fluid replacement. Med Sci Sports Exerc 39(2):377–390.