Most healthy adults need between 2,700 and 3,700 ml of total water per day. Women fall on the lower end at about 2,700 ml (91 ounces), and men on the higher end at about 3,700 ml (125 ounces). These figures from the National Academies of Sciences, Engineering, and Medicine include water from all sources: plain water, other beverages, and food.
What the Daily Totals Actually Mean
The 2,700 ml and 3,700 ml numbers represent total water intake, not just glasses of water you pour from a tap. Roughly 20% of your daily water comes from food, especially fruits, vegetables, soups, and yogurt. That means the amount you actually need to drink as liquid is closer to 2,200 ml for women and 3,000 ml for men. For reference, a standard glass holds about 250 ml, so that works out to roughly 9 glasses for women and 12 for men.
These are baseline recommendations for healthy, sedentary adults living in temperate climates. If you’re active, live somewhere hot, or are pregnant, your needs shift upward.
A Quick Way to Estimate Your Personal Need
A commonly used formula in clinical settings multiplies your body weight in kilograms by 30 ml. So a person weighing 70 kg (about 154 pounds) would need around 2,100 ml of fluid per day as a starting point. A person weighing 90 kg (about 198 pounds) would land at 2,700 ml.
This calculation gives you a personalized baseline, but it doesn’t account for exercise, heat, or illness. Think of it as a floor, not a ceiling.
How Much Children Need by Age
Children need significantly less water than adults, and the amount climbs steadily as they grow:
- Ages 1 to 3: about 1,000 ml (4 cups)
- Ages 4 to 8: about 1,200 ml (5 cups)
- Girls ages 9 to 13: about 1,400 ml (5 to 6 cups)
- Boys ages 9 to 13: about 1,600 ml (6 cups)
- Girls ages 14 to 18: about 1,600 ml (6 cups)
- Boys ages 14 to 18: about 1,900 ml (7 to 8 cups)
Infants under 6 months get all their fluid from breast milk or formula and should not be given plain water.
Adjustments for Pregnancy and Breastfeeding
The American College of Obstetricians and Gynecologists recommends pregnant women drink 8 to 12 cups of water per day, which translates to roughly 1,900 to 2,800 ml. Your blood volume increases substantially during pregnancy, and your body is also producing amniotic fluid, both of which drive higher fluid needs. Breastfeeding pushes the requirement even higher because you’re losing fluid through milk production.
Extra Water for Exercise
During physical activity, you lose water through sweat at a rate that varies widely depending on intensity, temperature, and your individual physiology. A practical guideline is to drink 200 to 300 ml every 15 minutes during exercise. That adds up to 800 to 1,200 ml per hour of activity, on top of your regular daily intake.
For a 30-minute jog, an extra 400 to 600 ml covers most people. For longer or more intense sessions, especially in the heat, you may need to replace electrolytes as well, not just water.
Hot Weather and Altitude
Heat and humidity increase sweat losses, sometimes dramatically. There’s no single number that applies to everyone, but if you’re sweating noticeably more than usual, your body is telling you to drink more. The same applies at high altitude, where you lose more water through breathing because the air is drier and you breathe faster to compensate for lower oxygen levels.
Coffee and Tea Still Count
A persistent myth holds that caffeinated drinks dehydrate you and shouldn’t count toward your daily fluid total. This isn’t accurate. Caffeine does have a mild diuretic effect, meaning it increases urine production slightly. But the fluid in a cup of coffee or tea more than offsets that small loss. At typical consumption levels, caffeinated beverages contribute positively to your hydration. The exception is very high caffeine doses taken all at once, which can cause a more noticeable increase in urine output, particularly if you’re not a regular caffeine drinker.
Signs You’re Not Drinking Enough
The simplest hydration check is urine color. Pale yellow to clear means you’re well hydrated. Dark yellow or amber signals you need more fluid. Other early signs of mild dehydration include dry mouth, fatigue, headache, and difficulty concentrating. By the time you feel genuinely thirsty, you’re often already slightly behind on fluids.
Can You Drink Too Much?
Yes, though it’s uncommon in everyday life. Your kidneys can process roughly 800 to 1,000 ml per hour. Drinking far beyond that rate, especially over a short period, can dilute the sodium in your blood to dangerous levels, a condition called hyponatremia. This is most often seen in endurance athletes who drink aggressively during long events without replacing electrolytes. For most people going about their normal day, the bigger risk is drinking too little, not too much. Just don’t force yourself to chug large volumes all at once.