In short: adults need about 2.0 litres of water a day (women) or 2.5 litres (men) from all sources, according to EFSA. About 20% comes from food. Exercise and heat add more. The calculator adds these up and shows how much to drink.
Built on EFSA values
The European reference intakes of total water, with pregnancy and breastfeeding.
Exercise and heat
An estimate for sweat lost during activity and in hot or dry weather.
Drinks and food
The total split into what you drink and what your meals already give you.
How to use it
- Choose woman or man, and pregnancy or breastfeeding if it applies.
- Enter your exercise in minutes per day and choose the climate.
- Read the total and the part from drinks. Spread it across the day.
How do I know I am drinking enough?
Thirst and urine colour are reliable everyday guides: pale yellow urine usually means you are well hydrated, dark yellow means you need more. Older adults feel less thirst and benefit from drinking at regular times.
Frequently asked questions
Is "8 glasses a day" right?
It is a rough rule. EFSA's values are 2.0 L for women and 2.5 L for men in total, including about 20% from food, so drinks provide roughly 1.6 L and 2.0 L. Needs vary with size, activity and climate.
Do coffee and tea count?
Yes. Coffee, tea, milk and other drinks count towards your water. Alcohol does not help hydration.
How much more do I need when I exercise?
Sweat losses vary widely, often 0.5–1.5 L per hour. The calculator adds about 0.6 L per hour of activity as a middle estimate. For long or hot sessions, drinks with electrolytes can help.
Can you drink too much water?
Yes, though rarely. Drinking very large amounts in a short time, for example during endurance events, can lower blood sodium (hyponatraemia). Drink to thirst rather than forcing large volumes.
What if my doctor limits my fluids?
Follow your doctor's advice. People with heart failure, some kidney diseases or other conditions may need to limit fluids, and this calculator does not apply to them.
Is anything stored?
No. The calculation runs in your browser and nothing is sent anywhere.
