Is 8 glasses of water a day necessary?

It is a rough guideline, not a rule. Eight 240 ml glasses is about 2 litres, which suits many people, but actual needs vary with weight, activity, and climate.

Does coffee dehydrate you?

No, not at normal intakes. The water in coffee more than offsets its mild diuretic effect, so it still counts toward fluid intake.

How do I know if I am drinking enough?

Pale-yellow urine and infrequent thirst are simple signs. Dark urine suggests you need more.

Healthy Habits

How Much Water Should You Drink a Day?

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"Drink eight glasses a day" is the advice everyone knows - but it is more of a rough slogan than a scientific rule. Your real needs depend on your body size, activity, and climate.

A better estimate

A practical guideline is about 30-35 ml of water per kilogram of body weight per day. For a 70 kg adult that is roughly 2.1-2.5 litres, before accounting for exercise. Get a personalized number from the Water Intake Calculator.

Add water for exercise and heat

Add roughly 350-500 ml of fluid for every 30-60 minutes of exercise, and more in hot or humid conditions or at altitude. Intense exercise sessions that make you sweat heavily increase needs further.

Do other drinks count?

Yes. Tea, coffee, milk, and water-rich foods (fruit, vegetables, soup) all contribute to total fluid intake. The mild diuretic effect of caffeine does not cancel out the water in your coffee. Plain water is still the best default because it has no calories or sugar.

Signs you are well hydrated

Pale-yellow urine (not dark, not completely clear)
Infrequent thirst
Normal energy and concentration

Can you drink too much?

Rarely, but drinking extreme amounts in a short time can dilute blood sodium (hyponatremia), which is dangerous. Spread intake through the day and drink to thirst rather than forcing large volumes at once.