Nutrition
Daily water intake
'Eight glasses a day' double-counts: about a fifth of your fluid comes from food. This separates total fluid from what you actually have to drink.
Result
Breakdown
Worth knowing
- About 20% of daily fluid comes from food, so the drinks figure is lower than the total.
- People with heart or kidney conditions may be on a fluid restriction — follow clinical advice over any calculator.
How this is calculated
Baseline is 35 ml/kg, plus ~350 ml per 30 minutes of exercise and a climate allowance. The US National Academies adequate intake figures (3.7 L men, 2.7 L women) are totals including food, which is the comparison most advice gets wrong.
Common questions
Is it really eight glasses a day?
That advice double-counts. The commonly cited adequate intake figures — about 3.7 L for men and 2.7 L for women — are totals including the water in food, which supplies roughly a fifth of it. This calculator separates total fluid from what you actually have to drink.
Do coffee and tea count?
Yes. Caffeine has a mild diuretic effect, but it does not come close to offsetting the fluid in the drink itself. So do milk, juice and most other drinks.
Can you drink too much water?
Yes, though it is uncommon. Drinking far beyond your needs can dilute blood sodium, which is why endurance athletes are warned about over-drinking during long events. Thirst and pale straw-coloured urine remain better day-to-day guides than any target.