Believe it or not, there’s not a perfect answer to the question of how much water a person should drink a day.
Many people believe anecdotal claims that all adults should drink eight, eight-ounce glasses of water or even as much as a gallon of water daily, but the answer isn’t quite that simple.
Based on the Dietary Reference Intakes for Americans (DRIs), adequate intake for males between the ages of 19–70 is about 3 liters of total fluid per day, or about 13 cups. The adequate intake level for women in the same age range is about 2.2 liters of total fluids per day, or about 9 cups.
The DRIs provide a good starting point, but the amount of water that you should drink per day varies based on many factors, including your age and gender, where you live or train, the weather, and the intensity and length of your exercise sessions. Since there’s no single right answer, you should use the guidelines as a starting point and monitor your hydration status to find the amount of water that works best for you each day.
Benefits of Proper Hydration
Water is an essential part of our bodies. The human body is made up of about 60–70% water, and even 2% dehydration can start having negative effects on the body.
Staying well hydrated helps:
Keep skin healthy
Clear waste products out of the body through urine, sweat, and bowel movements
Enhance exercise performance
Improve how well you tolerate heat
Support brain function
Factors That Affect How Much Water You Should Drink
Body weight and size
A larger body requires more water than a smaller one. Bigger bodies lose more water through sweat and require more water to maintain their body functions. A small study on American football players found that they had higher sweat losses than cross country runners working out in the same conditions. There are individual variations even in similarly sized people doing the same activities, but in general, bigger bodies may require more water.
Water is present in food, water, and all types of beverages. A diet high in fruits and vegetables provides more water naturally than a diet low in fresh foods, so you may need to drink less water if you eat more high-water foods. Conversely, a diet high in salt and low in fresh foods may increase the amount of water you need to drink.
High heat or humidity increases your fluid requirements because you sweat more than you do in cooler temps. More surprisingly, cold temperatures can also increase fluid requirements. You might not notice that you’re sweating, but your fluid needs are high while exercising in cold temperatures, too.
High altitude increases water loss through an increased rate of breathing and possibly increased sweating. You may not realize you’re sweating, but you’re losing water from your skin.
Length and intensity of workouts
A more gentle workout, such as a casual walk or a yoga class, may not make you sweat very much so it won’t increase your fluid needs greatly. A long workout, such as a long training run or a sports practice lasting a few hours, increases your fluid needs much more.
As mentioned above, men require about 4 cups more per day of fluids than women at baseline. In addition, the American College of Sports Medicine (ACSM) notes that women typically sweat less than men. This is due to women’s typically smaller body size and lower metabolic rates.
For adults from 19 up until age 70, fluid guidelines remain mostly the same. Elderly adults are at higher risk for dehydration because of a decreased sense of thirst.
Pregnancy or breastfeeding
Pregnant and lactating women have higher fluid needs than other women. Pregnant women need 2.3 liters per day of beverages, or about 10 cups per day. Women who are breastfeeding need even more at about 3.1 liters per day, or about 13 cups.
Water Needed Before, During, and After Exercise
According to the ACSM, fluid guidelines before, during, and after exercise are as follows:
Hydrate several hours before an event. The ACSM suggests drinking 5–7 milliliters (mls) per kilogram (kg) of body weight about four hours before your event or workout. To convert your weight in pounds to kilograms, divide by 2.2. For a 150-pound woman (about 68 kg), this would be about 340–475 mls or 11–16 ounces of water.
The amount of water and other beverages needed during exercise depends on each individual, the length of the workout, and the environment. It’s reasonable to drink a few ounces at pauses in activity throughout your workout, but avoid drinking so much you have a sloshy belly. To get a more exact idea, you could calculate your sweat rate.
To know how much water to drink after exercise, weigh yourself before and after exercise. Drink about 16 ounces for every pound you lost during the workout. You don’t have to replace the fluid you lost while exercising immediately, but make a conscious effort to drink more over the next several hours. If you regularly have a large difference between your before and after workout weights, you may need to increase the amount you drink during the workout, or consider sipping a sports drink while you exercise.
Registered Dietitian Tips to Increase Water Intake
Try these ideas to increase your water intake:
Keep a water bottle with you. If you keep a reusable water bottle with you as you move through your day, it should help remind you to drink more water. You could also set reminders on your phone to drink water at regular intervals if carrying a water bottle isn’t enough.
Consider flavoring your water naturally. Try infusing water with fruit such as oranges or strawberries or herbs such as basil or mint. Add a squeeze of citrus like lemon, lime, or grapefruit to your water bottle for a fresh taste. You could also try brewing herbal teas to increase your water intake, such as chamomile, mint, ginger, or hibiscus-flavored teas. Sparkling water may also help increase your water intake, and they’re available in a wide variety of flavors now.
Change your habits. Think of more triggers that will remind you to drink water. For example, you could make a new habit to drink 8 ounces of water from your coffee mug before having a cup of coffee, or drink a full glass of water as soon as you get out of bed in the morning. Place your water bottle on your desk, or take a break at set times during the work day to grab a bottle of water.
Remember that other liquids count. Though you should work on drinking water as your primary beverage, other liquids count toward your fluid goals. If you’re not a great water drinker yet, don’t despair. Teas, coffee, sparkling or flavored waters, dairy and dairy substitutes, and even high water content foods will help meet your fluid goals. Limit the amount of sugary drinks (soda, juice, sugary coffee beverages) you consume, but it’s OK to cut back gradually on these other drinks and replace them with water.
How Do I Know If I’m Dehydrated?
Thirst might help, but it might not be enough. It's well established that you're already 1–2% dehydrated when you feel thirst.
Check the color and volume of your urine. A large amount of light or pale yellow indicates good hydration status, while a small amount of dark colored urine shows that you need more water.
You could also weigh yourself before and after intense exercise sessions. A change in weight indicates some level of dehydration and that you should drink fluids to rehydrate.
Key Hydration Caveats
Follow thirst, but monitor other signs
Always drink when you feel thirsty, but keep an eye on your urine output and other signs. Thirst isn’t always the only indicator of hydration, especially for active people.
Limit sports drinks
Sports dietitians usually only recommend sports drinks when it’s hot or humid outside, or if your workout is over an hour and intense. Avoid drinking sports drinks all day, as they have too much sugar and salt to be used as a primary beverage by most healthy people. You could also try mixing low-sugar or no-sugar electrolyte tabs or powder with water during or after exercise.
Avoid drinking extreme amounts of water
Even if you’re in the middle of a hard workout or long training session, it’s possible to drink too much water. Hyponatremia is a fairly rare health condition, but it can occur as a result of drinking excessive water or not replacing enough sodium during endurance events such as a marathon.
Frequently Asked Questions
Is 4 liters of water per day too much?
Four liters is about 16.7 cups of water per day. This may be an appropriate amount of water for an active person, or someone in a hot or high-altitude environment. It’s probably not necessary for most people to drink that much water, but it’s likely safe.
Is a gallon of water per day too much?
A gallon of water is 128 ounces, or about 16 cups of water. A gallon of water per day is likely safe to drink for most people if it’s spread throughout the day. However, it’s not necessary to drink that much water unless you’re in a very hot, humid, or high-altitude environment or you’re doing intense exercise for long periods of time.
The Bottom Line
Remember, guidelines are a great starting point to help with your hydration goals but fluid needs vary based on many factors. Use thirst as a tool, but also monitor urine output and think through other factors that affect your water needs. Increasing the amount of water you drink per day is a worthy goal, but it’s OK to work your way up to your goals over time if you’re struggling to increase your water intake at first.