Most adults need about 2 to 3.7 litres of total water per day, depending on sex, body size, and activity level. That number includes water from everything you consume: drinks, coffee, tea, and food. If you’re looking for a simple drinking target, most women need roughly 1.5 to 2 litres of plain water, and most men need about 2 to 3 litres, with food covering the rest.
What the Official Guidelines Say
Two major health authorities set slightly different targets. In the U.S., guidelines suggest about 2.7 litres of total fluid per day for women and 3.7 litres for men. The European Food Safety Authority recommends 2.0 litres for women and 2.5 litres for men. Both figures include water from food, which typically accounts for about 20% of your daily intake. So the amount you actually need to drink is lower than those headline numbers.
For children, the targets scale with age. Kids aged 4 to 8 need about 1.6 litres total. By adolescence, boys need around 2.5 litres and girls about 2.0 litres. Pregnant women should aim for at least 2.3 litres total, and breastfeeding mothers need closer to 3.0 to 3.8 litres (roughly 16 cups) to compensate for the water used to produce milk.
Why “8 Glasses a Day” Isn’t Quite Right
The famous advice to drink eight glasses of water a day traces back to a 1945 recommendation from the U.S. Food and Nutrition Board, which suggested 2.5 litres of daily water intake. Two important details got lost along the way: the recommendation wasn’t based on any specific research, and it explicitly stated that most of that water could come from food. Over decades, the nuance vanished and the round number stuck. Eight glasses (about 1.9 litres) is a reasonable ballpark for many people, but it’s not a scientific threshold. Your actual needs could be higher or lower.
Factors That Change Your Needs
Exercise is the biggest variable. Sweat rates range from about one litre per hour during moderate activity to as much as three litres per hour during intense exercise in the heat. The general guidance for athletes is to drink 200 to 300 ml every 15 minutes during exercise, though the goal is to roughly match what you lose in sweat. For people with very high sweat rates (above 2 litres per hour), full replacement during exercise isn’t realistic because the stomach can only absorb about 1.2 litres per hour. Rehydrating after your workout matters just as much.
Hot or humid weather increases water loss through sweat even if you’re not exercising. Altitude and dry indoor air (especially heated or air-conditioned spaces) speed up water loss through breathing and skin evaporation. Illness involving fever, vomiting, or diarrhea can dramatically increase your fluid needs in the short term. And body size plays a straightforward role: a larger person needs more water than a smaller one.
How to Tell if You’re Drinking Enough
Rather than obsessing over a specific number of litres, your body gives you two reliable signals. The first is thirst. For most healthy adults, drinking when you’re thirsty and with meals covers your needs.
The second, more objective signal is urine color. Pale, light yellow urine with little odor means you’re well hydrated. Slightly darker yellow suggests you need more fluids. Medium to dark yellow, especially in small amounts with a strong smell, signals dehydration. You don’t need to aim for completely clear urine; that can actually indicate you’re overdoing it. A light straw color is the sweet spot.
Can You Drink Too Much Water?
Yes. Drinking too much water in a short period dilutes the sodium in your blood, a condition called hyponatremia. Symptoms can develop after drinking roughly 3 to 4 litres within an hour or two. As a safety guideline, avoid drinking more than about a litre per hour. This is most relevant during endurance sports, where people sometimes force fluids beyond what their body needs, or during water-drinking challenges. Under normal circumstances, healthy kidneys can handle quite a lot of water spread across the day. The risk comes from large volumes consumed rapidly.
Foods That Count Toward Your Intake
About 20% of your daily water comes from food. Some foods contribute far more than others. Cucumbers, watermelon, strawberries, lettuce, and celery are over 90% water by weight. Soups, yogurt, and cooked grains like oatmeal and rice also add meaningful amounts. Coffee and tea count toward your fluid intake as well. While caffeine has a mild diuretic effect, the water in a cup of coffee more than offsets it, so your morning coffee isn’t dehydrating you.
If your diet is heavy on fresh fruits, vegetables, and soups, you may need less plain water than someone eating mostly dry, processed foods. There’s no need to track this precisely, but it’s worth knowing that your water bottle isn’t your only source.
A Practical Daily Target
If you want a simple number to work with: aim for about 1.5 to 2 litres of water per day if you’re a woman, and 2 to 2.5 litres if you’re a man, adjusting upward on days you exercise, spend time in the heat, or feel thirstier than usual. Sip throughout the day rather than chugging large amounts at once. Keep a water bottle visible as a reminder, and let your thirst and urine color guide you from there. The exact number matters less than building a consistent habit of drinking regularly.