How Much Water Should You Drink a Day?

According to the National Academies, an adequate daily intake of total water is about 3.7 liters (roughly 15.5 cups) for men and about 2.7 liters (roughly 11.5 cups) for women. That total includes water from all drinks and foods, not just plain water. Because food typically supplies around 20% of it, most people need to drink less than those headline numbers, and thirst is a reliable guide for many healthy adults.

What these numbers really mean

The National Academies’ figures are Adequate Intakes for healthy adults in temperate climates. They reflect what healthy people typically consume rather than a strict minimum. In their report, the experts noted that this works out to about 3.0 liters (about 13 cups) of beverages a day for men and about 2.2 liters (about 9 cups) for women, with the rest coming from food.

These are averages for groups, not personal prescriptions. Your own needs depend on your body size, activity, climate, health and what you eat.

What about eight glasses a day?

The familiar “eight 8-ounce glasses” rule is easy to remember, but it isn’t based on strong scientific evidence. For some people it’s roughly right; for others, especially active people or those in hot climates, it may fall short. And plenty of people get enough fluid from a mix of drinks and water-rich foods without counting glasses at all.

Signs you’re getting enough

For most healthy adults, the body is good at signaling its needs:

• You rarely feel very thirsty.
• Your urine is mostly pale yellow, although some vitamins and foods can change its color.
• You feel alert rather than headachy or dizzy.

Signs you may need more fluid include dark yellow urine, a dry mouth, headache, fatigue, dizziness or urinating less often than usual. Older adults may feel less thirsty even when their bodies need water, so drinking regularly with meals and snacks can help.

When you need more

Your needs rise in several situations:

• Hot or humid weather, and high altitude.
• Exercise and physical work, especially long sessions with heavy sweating.
• Illness with fever, vomiting or diarrhea.
• Pregnancy and breastfeeding.

During long or intense exercise in the heat, or during illness, you may need to replace sodium and other minerals along with water. Our guide to electrolytes explains when that matters.

Foods and drinks that count

Almost everything you drink adds to your total, and many foods chip in too:

• Water, still or sparkling, is the simplest choice.
• Milk and fortified soy drinks count and bring protein and calcium.
• Coffee and tea count as well. Caffeine nudges urine output slightly, but moderate amounts still add to your fluid intake.
• Soups and broths are mostly water.
• Fruits and vegetables such as cucumber, lettuce, watermelon, strawberries, oranges and tomatoes are mostly water, often 85% or more.

Sugary drinks like soda, sweet tea and many fruit drinks provide fluid as well, but they can add a lot of sugar. Our added sugar guide explains how to keep that in check, and the CDC encourages choosing water over sugary drinks.

Can you drink too much water?

It’s uncommon, but yes. Drinking very large amounts in a short time, which occasionally happens during marathons and other endurance events, can dilute the sodium in your blood and lead to a dangerous condition called hyponatremia. Some people, including those with heart failure or advanced kidney disease, may be told by their doctor to limit fluids. If you have a medical condition, follow your care team’s guidance on how much to drink.

Easy hydration habits

1. Keep a refillable bottle within reach at work, in the car or in your bag.
2. Drink a glass of water with every meal.
3. Flavor water with lemon, cucumber, mint or a few frozen berries.
4. Sip before, during and after exercise.
5. Eat plenty of fruits and vegetables, which bring water along with nutrients.
6. If you’re trying a schedule like intermittent fasting, keep drinking water during fasting hours.

The bottom line

The National Academies suggest about 3.7 liters of total water a day for men and 2.7 liters for women, from all foods and drinks combined. Most people meet their needs by drinking when thirsty, having fluids with meals and eating water-rich produce. Drink more in the heat, during exercise, when you’re sick, and while pregnant or breastfeeding, and follow medical advice if you have a condition that affects fluid balance.