Most healthy adults need about 11.5 to 15.5 cups of total water per day, depending on sex, body size, and activity level. That total includes water from all sources: plain water, other beverages, and food. About 20 to 30% of your daily water comes from food, which means you need roughly 8 to 12 cups from drinks alone. These numbers shift based on your weight, how active you are, your age, and whether you’re pregnant or breastfeeding.
A Simple Formula Based on Body Weight
General guidelines are a starting point, but your body size matters. A widely used formula from the University of Missouri makes it easy: take your body weight in pounds, divide it in half, and drink that many ounces of water per day. A 160-pound person would aim for about 80 ounces, or 10 cups. A 200-pound person would target 100 ounces, roughly 12.5 cups.
This formula gives you a baseline for a typical day with moderate activity and a temperate climate. If you exercise, live somewhere hot, or are recovering from illness, you’ll need more on top of that number.
How Exercise Changes Your Needs
During physical activity, your body loses water through sweat at rates that vary widely depending on intensity, temperature, and your individual physiology. The Korey Stringer Institute, a leading sports safety research center, recommends drinking about 200 to 300 milliliters (roughly 7 to 10 ounces) every 15 minutes during exercise. That works out to about 28 to 40 ounces per hour of activity.
After a workout, the goal is to replace more than what you lost. The standard recommendation is to drink 150% of the body weight you lost during exercise. In practical terms, for every 2.2 pounds (1 kilogram) lost during a session, you’d drink about 1 liter (4 cups) of fluid afterward. Weighing yourself before and after exercise is the most reliable way to gauge your sweat losses.
Pregnancy and Breastfeeding
Breastfeeding increases water needs significantly because your body is producing roughly 700 milliliters (about 3 cups) of milk per day. The European Food Safety Authority recommends that breastfeeding women add an extra 700 milliliters to their daily intake, bringing the total to about 2,700 milliliters (11.5 cups) of total water per day. During pregnancy, fluid needs also increase, though by a somewhat smaller margin, to support increased blood volume and amniotic fluid.
Why Older Adults Need to Pay Extra Attention
As you age, your body becomes less reliable at signaling thirst. Research published in the National Institutes of Health found that healthy older men who were deprived of water for 24 hours reported no significant increase in thirst or mouth dryness compared to younger participants. The body’s ability to detect rising concentration in the blood simply weakens with age, which makes dehydration a common and sometimes serious issue for people over 65.
The recommended fluid intake from drinks for older adults is about 6.5 cups per day for women and 8 cups per day for men. Because thirst is an unreliable guide in this age group, drinking on a schedule or keeping water visible throughout the day is more effective than waiting until you feel thirsty.
Do Coffee and Tea Count?
Yes. Caffeinated beverages contribute to your daily fluid intake despite caffeine’s mild diuretic effect. The fluid in coffee, tea, and similar drinks offsets the small increase in urine production that caffeine causes. The one exception is consuming unusually high doses of caffeine all at once, especially if you’re not a regular caffeine drinker, which can temporarily increase urine output enough to matter. For most people drinking a few cups of coffee a day, those cups count toward your total.
How to Tell If You’re Drinking Enough
Urine color is the simplest, most reliable hydration check you can do throughout the day. A standard hydration scale breaks it down like this:
- Pale yellow or nearly clear: Well hydrated. You’re on track.
- Slightly darker yellow: Mildly dehydrated. Time to drink a glass or two.
- Medium to dark yellow: Dehydrated. You need to increase your fluid intake now.
- Dark amber with a strong smell, in small amounts: Very dehydrated. Drink water steadily over the next few hours.
Keep in mind that certain vitamins (especially B vitamins) can turn urine bright yellow regardless of hydration, and some medications affect color as well. If you’re taking a multivitamin, rely on urine volume and frequency as additional clues. Urinating every two to four hours in reasonable amounts, with a light color, generally indicates good hydration.
Where Your Water Actually Comes From
Not all of your water needs to come from a glass. In a typical Western diet, 20 to 30% of total water intake comes from food. Fruits and vegetables are especially water-dense: cucumbers, watermelon, oranges, and lettuce are all over 90% water by weight. Soups, yogurt, and cooked grains also contribute meaningful amounts. The remaining 70 to 80% comes from beverages of all kinds, including water, milk, juice, coffee, and tea.
This means that if your daily target is around 100 ounces of total water, roughly 70 to 80 ounces need to come from what you drink, and the rest is covered by a reasonably balanced diet. If you eat very few fruits and vegetables, you’ll want to compensate by drinking a bit more.