Most healthy adult men need about 3,700 ml of total water per day, while women need about 2,700 ml. Those numbers, set by the Institute of Medicine, include all water sources: plain drinking water, other beverages, and the moisture in food. In terms of fluids alone (excluding food), the target drops to roughly 3,000 ml for men and 2,200 ml for women.
What “Total Water” Actually Means
The 3,700 ml and 2,700 ml figures aren’t how much you need to pour from a bottle. A significant portion of your daily water comes from the food you eat. Fruits, vegetables, soups, yogurt, and cooked grains all contain water that counts toward your total. In the U.S., food moisture typically covers about 17% to 25% of an adult’s total water intake. In countries with more soup- and produce-heavy diets, like France or China, food can contribute 36% to 40%.
So if you’re a woman aiming for 2,700 ml total and roughly 20% comes from food, that leaves about 2,200 ml (around 9 cups) to get from drinking water, coffee, tea, juice, or other beverages. For men, it’s about 3,000 ml (around 13 cups) of fluids. Coffee and tea do count. Despite the old myth, their mild diuretic effect doesn’t cancel out the water they contain.
How Exercise Changes the Target
Physical activity can increase your needs substantially. During moderate to intense exercise, the general guideline is to drink 200 to 300 ml every 10 to 20 minutes to replace sweat and urine losses. That can add up to 600 ml to 1,800 ml per hour of hard training. The goal is to keep body weight loss below 2% during a session, since losses beyond that threshold start to impair performance and concentration.
If you exercise for an hour most days, adding 500 to 1,000 ml above your baseline is a reasonable starting point. Longer or more intense sessions in warm weather push that number higher.
Adjustments for Heat and Altitude
Hot and humid environments increase sweat rates, sometimes dramatically. But altitude is an underappreciated factor. At elevations up to 4,000 meters (about 13,000 feet), respiratory water loss alone can jump by up to 1,900 ml per day in men and 850 ml in women, simply because you breathe harder in thinner air. Urinary losses also rise by roughly 500 ml per day at altitude. For mountain activities, the recommendation is 400 to 800 ml per hour, ideally with a small amount of sodium added to the water.
Pregnancy and Breastfeeding
Pregnant women are generally advised to increase total water intake to about 2,300 ml of fluids per day (slightly above the standard female recommendation). The jump is more significant during breastfeeding. Producing breast milk uses roughly 700 ml of water daily, so the European Food Safety Authority recommends breastfeeding women aim for a total of 2,700 ml of fluids per day, which is about 700 ml above the usual target.
How Much Children Need
Children’s water needs scale with body weight rather than following a single number. For infants weighing 3.5 to 10 kg, the requirement is about 100 ml per kilogram of body weight per day. So a 7 kg baby needs roughly 700 ml total. For children between 11 and 20 kg, it’s 100 ml per kg for the first 10 kg plus 50 ml for each additional kg. A 15 kg toddler, for example, would need about 1,250 ml per day.
For children over 20 kg, the formula is 1,500 ml for the first 20 kg plus 20 ml for every additional kg, up to a maximum of about 2,400 ml at once. A 30 kg child would need roughly 1,700 ml daily.
How to Tell If You’re Drinking Enough
Urine color is a surprisingly reliable self-check. Research on over 800 urine samples found that a color rating of 4 or higher on a standard 8-point chart (think apple juice or darker) detected underhydration with about 88% sensitivity. In practical terms: pale yellow, like lemonade, signals good hydration. Darker shades suggest you need more fluids. Clear and colorless urine usually means you’re overhydrating, which isn’t harmful in moderate amounts but isn’t necessary either.
Thirst is another reasonable guide for most healthy adults, though it tends to lag behind actual fluid needs during exercise and in older adults whose thirst signals weaken with age.
Can You Drink Too Much?
Yes. Healthy kidneys can process about 1,000 ml (one liter) of fluid per hour. Consistently exceeding that rate over several hours can dilute sodium levels in the blood to dangerous levels, a condition called hyponatremia. This is rare in everyday life but does occur in endurance athletes or people who force-drink large volumes in a short window. Spreading your intake throughout the day rather than gulping large amounts at once keeps you well within your kidneys’ processing capacity.