We investigated the claims behind the recommended water intake of eight 8-oz. glasses per day.

By Lauren Wicks
April 04, 2019

There’s a lot of disagreement within the nutrition sphere, but there is one health claim that seems to withstand the test of time—the “8x8” rule. It’s widely held that we should be consuming 64 ounces of water per day, or eight eight-ounce glasses of water. But is there actually any research behind this recommendation? More importantly, how much water should we really be drinking each day? We decided to find out.

8x8 Rule: Fact or Fiction?

It’s thought that the water intake rule originated loosely from a recommendation made by the National Academy of Medicine in 1945—then called the Food and Nutrition Board. The organization advised that the average person should consume 1 mL water for every calorie consumed. This equates to about 64 ounces a day on a 1,900 calorie diet—close to current USDA recommendation of 2,000 calories per day.

A large review of water intake-related studies found no scientific reports concluding this rule is as good as law. The author of this review actually found several studies noting the potential dangers of following the “8x8” recommendation. For one, it may accidentally induce hyponatremia, a condition caused by drinking too much water. Secondly, it can leave people feeling guilty if they aren’t meeting that benchmark.

Recommended Water Intake

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As it turns out, there really isn’t a one-size-fits-all answer recommendation for water intake. While the current Dietary Reference Intakes advise an intake of approximately 9 cups per day for women and 13 cups for men, fluid requirements can also vary based on age, activity level, and even your climate.

Here’s another piece of the puzzle: we consume water from food and other beverages as well during the day. In fact, moderate consumption of beverages like coffee and tea actually do not have a negative impact on our hydration levels—and can be considered a factor in daily water intake. Additionally, produce like watermelon, celery, and iceberg lettuce are high in water content and contribute to our intake. Even meat, fish, and eggs can contribute to water intake.

When it comes to drinking water, it’s best to just go with your gut. Drink when you’re thirsty and stop when you’re not. Keeping a reusable water bottle with you is an easy way to stay hydrated—and it can also help prevent you from filling up on soda or other sugary beverages. (Don’t worry, sparkling water counts towards your goal too!)

Benefits of Drinking Water

While the CDC doesn’t have recommendations for how much water to drink, they encourage choosing plain water over flavored drinks as often as possible. Water’s hydrating effect helps keep your digestive system regular, promotes healthy skin, prevents headaches, and keeps your mind sharp. Some studies associate regular water consumption with a decreased risk for several chronic diseases.

The most important benefit of all, however, is that water keeps us alive. We can’t survive more than a few weeks without it.

Looking for easy ways to boost your water intake?

How to Know If You’re Dehydrated

While intense thirst is the most obvious red flag, there are several other major signs that could mean you need to up that water intake. Because the brain is composed of 80 percent water, headaches are actually one of the first signs of dehydration. Dehydration can cause brain shrinkage, reduced oxygen and blood flow, and ultimately painful swelling and inflammation.

Dry skin, eyes, or mouth, as well as dark urine, are also typical side effects of not drinking enough water. Low energy, muscle cramps or spasm, and feeling disoriented are common side effects after a prolonged period of inadequate water consumption. You can even become dehydrated in extreme temperatures—both hot and cold—so it’s important to adjust your water intake based on your climate.

Can Drinking More Water Help You Lose Weight?

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Ah, the age old question. Lucky for us, the CDC does indeed tout water as a weight loss (and management) tool. Some studies have found links between water consumption and a metabolism boost, estimating that drinking two liters of water—just over 68 ounces—per day could lead to an additional 96 calories burned.

Our hydration status has an impact on our hunger cues, meaning we can often mistake hunger for thirst if we are dehydrated. Since some of our water intake comes from food, our brains can get tricked into thinking we’re hungry when we just need a big glass of H2O. Drinking water approximately 30 minutes before meal times can even help you consume fewer calories during meals.

However, drinking more water isn’t a magical weight loss tool and shouldn’t be used in isolation. Consuming a healthy diet and participating in regular exercise are always your best bets for weight loss and maintenance.

Can You Drink Too Much Water?

Yes—and overconsumption of water can be a serious health risk. While uncommon, hyponatremia is a condition induced by excessive water consumption where blood sodium levels become too low. Symptoms of hyponatremia include brain fog, bloating, headaches, and nausea.

If your urine is consistently clear and your bathroom visits each day are in the double digits, you may be overdoing it. Remember: there are plenty of factors that count toward water intake. While keeping a water bottle by your side during the day is an easy way to hydrate, the food you eat also contributes. Forcing yourself to drink water during the day—especially if you aren’t thirsty—simply isn’t healthy.

 

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