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You may have heard that you should aim to drink eight 8-ounce glasses of water per day. How much you should actually drink is more individualized than you might think.

The Institute of Medicine (IOM) looked at survey data to find out about Americans’ average daily water intake. Based on this data, they published recommendations that they called adequate intakes (AIs) in a 2005 study.

Doctors still refer to these recommendations today. They include:

  • 3.7 liters per day for men, including about 3 liters (approximately 13 cups) in the form of beverages
  • 2.7 liters per day for women, including about 2.2 liters (approximately 9 cups) in the form of beverages

AIs are based on the median water intake from U.S. survey data, and some people seem to do fine with less water. A wide range of intakes is typical in a population. For instance, physically active people or those who live in hotter environments will require a higher intake of water.

This range shows that the answer to exactly how much water you should drink isn’t so simple.

While the eight glasses rule is a good start, it isn’t based on solid, well-researched information.

Your body weight is made up of 60 percent water. Every system in your body needs water to function. Your recommended intake is based on factors including your gender, age, activity level, and whether you’re pregnant or breastfeeding.

Adults

The current IOM recommendation for people ages 19 and older is around 131 ounces for men and 95 ounces for women. This refers to your overall fluid intake per day, including anything you eat or drink that contains water, like fruits or vegetables.

Of this total, men should get around 13 cups from beverages. For women, it’s 9 cups.

Children

Recommendations for kids have a lot to do with age:

  • Children between 4 and 8 years old should drink 40 ounces per day, or 5 cups.
  • This amount increases to 56 to 64 ounces, or 7 to 8 cups, by ages 9 to 13.
  • For ages 14 to 18, the recommended water intake is 64 to 88 ounces, or 8 to 11 cups.

Pregnant or breastfeeding women

If you’re pregnant or breastfeeding, your recommendations change.

The IOM recommends that pregnant women of all ages should aim to get 80 ounces, or 10 cups of water, each day.

Breastfeeding women may need to up their total water intake to 104 ounces, or 13 cups.

DemographicTotal daily recommended amount of water from drinks
children 4–8 years old5 cups, or 40 oz.
children 9–13 years old7–8 cups, or 56–64 oz.
children 14–18 years old8–11 cups, or 64–88 oz.
men 19 years and older13 cups, or 104 oz.
women 19 years and older9 cups, or 72 oz.
pregnant women10 cups, or 80 oz.
breastfeeding women13 cups, or 104 oz.

Other considerations

You may also need to drink more water if you:

  • Climate or altitude. You may need more water if you live in a hot climate or at an elevation greater than 8,200 feet above sea level.
  • Exercise. If you exercise often, the American Council on Exercise recommends you drink 17 to 20 ounces of water 2 to 3 hours before you exercise. They also recommend you drink an additional 8 ounces of water just before and after working out. You may need to add even more if you work out for longer than an hour.
  • Fever, vomiting, or diarrhea. You should also drink more water when you have a fever, vomiting, or diarrhea, because your body loses more fluids than usual. Your doctor may even suggest taking drinks with electrolytes to keep your electrolyte balance more stable.

Water is important for most processes your body goes through in a day. When you drink water, you replenish your stores. Without enough water, your body and its organs can’t function properly.

The Centers for Disease Control and Prevention (CDC) lists the following benefits of drinking water:

  • keeping your body temperature within a normal range
  • lubricating and cushioning your joints
  • protecting your spine and other tissues
  • helping you eliminate waste through urine, sweat, and bowel movements

Drinking enough water can also help you look your best. For example, a 2018 research review looked at the ways that water can keep your skin looking healthy.

The skin is your body’s largest organ. When you drink plenty of water, you keep it healthy and hydrated.

Drinking too little or too much water both have risks.

Dehydration

Your body is constantly using and losing fluids through actions like sweating and urinating. Dehydration happens when your body loses more water or fluid than it takes in.

Symptoms of dehydration can range from being extremely thirsty to feeling fatigued. You may also notice you aren’t urinating as often or that your urine is dark.

Signs of dehydration in children listed by Medline Plus include:

  • a dry mouth and tongue
  • a lack of tears while crying
  • fewer wet diapers than usual

Dehydration may lead to:

You can treat mild dehydration by drinking more water and other fluids.

If you have severe dehydration, you may need treatment at the hospital. Your doctor will likely give you intravenous (IV) fluids and salts until your symptoms go away.

Hyponatremia

Drinking too much water may be dangerous for your health as well.

When you drink too much, the extra water can dilute the electrolytes in your blood. Your sodium levels decrease and can lead to what is called hyponatremia.

Symptoms include:

When hyponatremia is caused by drinking too much water, it’s sometimes known as water intoxication hyponatremia. Water intoxication hyponatremia is uncommon.

People with a smaller build and children are at a higher risk of developing this condition. So are active people, like marathon runners, who drink large quantities of water in short periods of time.

If you’re at risk due to drinking large quantities of water for exercise, consider drinking a sports drink that contains sodium and other electrolytes to help replenish the electrolytes you lose through sweating.

Staying hydrated goes beyond just the water you drink. The Better Health Channel estimates that foods make up around 20 percent of your total fluid requirements each day. Along with drinking your 9 to 13 daily cups of water, try to eat lots of fruits and vegetables.

Some foods with high water content include:

You may be able to meet your water intake goal by drinking when you’re thirsty and with your meals.

If you need some extra help consuming enough water, check out these tips for drinking more:

  • Try carrying a water bottle with you wherever you go, including around the office, at the gym, and even on road trips. Amazon has a good selection of water bottles.
  • Focus on fluids. You don’t have to drink plain water to meet your hydration needs. Other good sources of hydration include milk, tea, and broth.
  • Skip sugary drinks. While you can get fluid from soda, juice, and alcohol, these beverages have high calorie contents. It’s still smart to choose water whenever possible.
  • Drink water while you’re out to eat instead of ordering another beverage. You can save some cash and lower the total calories of your meal too.
  • Add some flair to your water by squeezing in fresh lemon or lime juice.
  • If you’re working out hard, consider drinking a sports drink that has electrolytes to help replace the ones you lose through sweating. Shop for sports drinks.