Two litres is a rule of thumb, not a law. How much water you really need depends on weight, weather, exercise and food. Here is how to find your own figure.
In short
- Guideline for adults: about 1.5 litres to drink, plus roughly 1 litre from food.
- Rule of thumb: 30 to 35 millilitres per kilogram of body weight, everything added up.
- Heat, exercise and breastfeeding raise your needs by half a litre to a litre per hour of exertion.
- You can drink too much as well: more than a litre an hour over a longer period is too much.
Where the two litres come from
The German Nutrition Society (DGE) gives about 1.5 litres of drinking fluid a day for adults. On top of that comes roughly a litre of water from solid food, mainly from fruit, vegetables, soups and dairy products, and a small remainder that the body produces itself during metabolism. Together that makes a good 2.5 litres flowing through you every day. The famous “two litres of water” are therefore a simplification that suits many people and is too much or too little for others.
The formula for your own figure
A calculation by body weight is more practical: 30 to 35 millilitres per kilogram. A person weighing 70 kilograms ends up with 2.1 to 2.45 litres of total intake. Subtract the litre from food and 1.1 to 1.45 litres remain to drink. If you eat little fruit and vegetables, you drink correspondingly more. The Water intake calculator does this sum for you, including weather and exercise.
What raises your needs
- Heat: On hot days you lose clearly more through your skin and breath, often an extra half litre to a litre.
- Exercise: Every hour of endurance exercise costs 0.5 to 1 litre of sweat, more in the heat.
- Pregnancy and breastfeeding: Women who are breastfeeding need roughly 0.25 to 0.7 litres more per day.
- Fever, diarrhoea, vomiting: Here every cup counts. With children and older people, act early.
- Dry air: Air conditioning, heating and aeroplanes draw moisture from the body without you noticing.
Can you drink too much?
Yes. The kidneys can handle about 0.8 to 1 litre per hour. If you drink clearly more than that for hours without losing salt, you dilute your blood. This is rare, but it happens to marathon runners and to people who drink litres on principle. For everyday life that means: spread your amount over the day instead of catching up in the evening.
How to tell that it is right
The simplest test is the colour of your urine: pale yellow is good, dark yellow means drink more, clear as water means you can ease off. Thirst is a reliable signal in young, healthy people. In older people the sense of thirst fades, so a fixed routine helps more there than waiting for thirst. More in the article Signs of dehydration.
Try it out
Water intake calculatorWeight, age, weather, activity: your personal guideline in litres and glasses.Drink trackerTap the glass, see your progress through the day, keep your streak. Everything stays in your browser.Frequently asked questions
Do coffee and tea count towards my intake?
Yes. Caffeine has only a weak diuretic effect, and in habitual drinkers practically none. Coffee and tea count fully towards your fluid balance. Alcohol does not.
Do I have to drink on an empty stomach in the morning?
It does no harm and helps many people get going, because about half a litre is lost overnight. It is not a miracle cure.
What about sparkling water, does it count the same?
Yes, carbonation does not change the amount of fluid. If it fills you up faster, you sometimes drink less overall, and that is the only catch.
Share
