“Stay well-hydrated” is one of those time-tested pieces of nutritional advice you’ve been hearing your whole life — and likely still fail to follow. In a national survey of 2,000 American adults conducted by OnePoll for the brand Evian, less than one-quarter reported drinking eight or more glasses of water a day.

Why are all those fluids so critical? Well, according to the Centers for Disease Control and Prevention (CDC) they play a role in regulating body temperature, mood, and cognition. And, according to the Sleep Foundation, being well-hydrated may lead to better sleep.

But hydration can be surprisingly tricky. Most of us don’t think to drink until we feel thirsty — and by then, we may already be dehydrated. And the effects of dehydration go beyond thirst. Even mild dehydration can lead to fatigue, dizziness, headaches, and muscle cramps according to the Cleveland Clinic. Scientific literature indicates that cognitive function can take a hit when you’re running a mere 1 to 2 percent low on bodily fluids. (So swigging some H20 may be a good way to fight off brain fog!)

Adding to the confusion is the fact that there is no recommended dietary allowance (RDA) for water or fluids. You may have heard the old adage that you should have eight 8-ounce (oz) glasses of water each day, but hydration needs vary by gender, activity level, and even the climate. Plus, roughly 20 percent of our fluids come from the food we eat.

So how do you know how much you should aim for? While the recommendation to drink eight 8-oz glasses of fluid per day is certainly a good starting point, it’s mostly used because it’s so easy to remember, but it is not the most recent or accurate measure. The gold standard of hydration comes from the National Academies of Sciences, Engineering, and Medicine, which recommends that women get about 2.7 liters (L) of fluid per day and men get about 3.7 L per day. About 20 percent of that comes from the foods you eat, so that leaves about 2.2 L (nine 8-oz cups) for women and 3.0 L (thirteen 8-oz cups) for men coming from the fluids you drink.

While good ol' H20 — bottled or tap — is your best bet, it’s not the only beverage most of us are drinking in a day. Coffee is the third most popular beverage in the world (after water and tea), according to National Geographic, and if you’ve ever brewed it, you know that it is mostly water. But because caffeine is a diuretic (it’ll send you to empty your bladder more often), there is a persistent belief that coffee isn’t as effective as other beverages when it comes to meeting your hydration needs — or may even have the opposite effect.

There is plenty of evidence that drinking coffee is good for your health in general. The purported benefits of being a regular coffee drinker (between three to five 8-oz cups a day) include a lower risk of diabetes, cardiovascular disease, certain types of cancer, and Alzheimer’s and Parkinson’s diseases, according to Harvard Medical School. According to the National Coffee Association 62 percent of Americans kick their day off with a cup of coffee (or three), so it would be helpful to know if those fluids are helping us meet our hydration goals or not. Here is everything you need to know about coffee and hydration.

Water vs. Coffee: How Do They Compare?

Because the caffeine in regular coffee can have a slight diuretic effect, many believe that coffee is dehydrating, but that’s not actually the case. While drinking caffeinated coffee will cause a slight increase in urine excretion, it won’t cause you to lose more fluid than you’re getting from the coffee itself, according to the Mayo Clinic. That said, you won’t be getting the same fluid benefit cup-for-cup as you would from water. For example, a study published in September 2015 in the Journal of Science and Medicine in Sport found that for an average intake of about 300 milligrams (mg) of caffeine daily, about 15 percent of the fluid was lost. That means for each 8-oz cup of coffee (which has approximately 96 mg of caffeine, per Mayo Clinic), you can count a little less than 7 of those ounces toward your fluid intake. Water is still your best bet for getting the majority of your fluid each day though.

Nutrition Facts of Coffee

Coffee can be a low-calorie addition to any healthy diet. An 8-oz cup of black coffee has just two calories, and no fat or carbs, according to the U.S. Department of Agriculture (USDA). It contains trace amounts (2 percent or less of the daily value) of some minerals, but not enough to be significant. The main health benefits of coffee come from antioxidants and polyphenols found in the beans. Keep in mind that it’s generally what gets added to a cup of coffee that makes it a less-than-ideal nutritional choice, so a cup of coffee that’s packed full of cream and sugar won’t fit the same low-calorie profile as a cup of black coffee and may derail your overall health goals.

What About Coffee Makes It Hydrating?

Despite its slight diuretic effect, it shouldn’t be super surprising that, when consumed in moderation, a portion of coffee can be counted toward your fluid intake. After all, it is made with water!

Coffee vs. Tea: Which Is More Hydrating?

In moderation, coffee and tea can both be counted, at least in part, toward your hydration goal. Cup-for-caffeinated-cup, coffee contains more caffeine than all varieties of tea. This means that tea is technically a bit more hydrating than coffee, especially if you opt for a naturally caffeine-free tea or a low-caffeine variety, like green tea. Decaf coffee and tea are both almost completely devoid of caffeine and would be equally hydrating as a result.

Types of Coffee: How Hydrating Are They?

There are so many different types of coffee to choose from, and your personal preference will affect how much hydration you’ll get from your brew. Two main factors dictate how much hydration you’ll be getting: the amount of caffeine and the volume of the beverage. For example, according to Mayo Clinic, an 8-oz cup of regular brewed coffee contains about 96 mg of caffeine while the same sized cup of decaffeinated brewed coffee contains only 2 mg of caffeine. This means, while you’ll be getting about 7 oz of hydration from the regular coffee, you’ll be getting the full 8 oz of fluid from the decaf. Caffeinated instant coffee falls somewhere in between, with 62 mg of caffeine per 8-oz serving. Similarly, a 1-oz serving of espresso contains about 64 mg of caffeine, which gives it almost as much diuretic power as a full 8 oz of caffeinated coffee, but since that’s all packed into only 1 oz of fluid, you’re really not getting any hydration from a shot of espresso.

Health Benefits of Coffee Beyond Hydration

According to Mayo Clinic, up to 400 mg of caffeine is safe to consume each day. This would be equivalent to about four 8-oz mugs daily or 32 oz in total. Beyond the energy jolt that so many seek, coffee may actually offer a host of health benefits when consumed in moderation (at or under that 400-mg-per-day mark). In fact, Harvard points out that the antioxidants in both caffeinated and decaffeinated varieties alike can have anti-inflammatory effects and, when consumed in moderation, may help decrease risk of diseases such as type 2 diabetes and certain types of cancer.

Tips for Enjoying Coffee to Maximize the Perks

Wondering if there’s a “best practice” to get the most out of your java? While there’s no one perfect way to enjoy your coffee, making small tweaks to your current routine could make a big difference nutritionally. For example, adding items like sugar, sweeteners, or processed creamers can make a naturally low-calorie and relatively healthy beverage into a chemical-filled calorie-bomb. To maximize the perks you’ll get from a cup of coffee, enjoy it black or with a small (preferably measured) amount of milk or cream. If you enjoy coffee that is flavored with syrup, try adding spices such as cinnamon or nutmeg to the grounds before you brew instead. This will add flavor without all of the calories and sugar that flavored syrups bring. And, as with anything, you can enjoy too much of a good thing, so keep coffee to four cups or fewer per day and remember to switch to decaf later in the day, especially if you have trouble sleeping.

Should You Drink Coffee to Stay Hydrated?

If being well-hydrated is one of your personal health goals, water is still going to be your best bet. However, if, like most people in the United States, you enjoy a few cups of coffee each day, feel free to continue doing just that — and start counting a portion of it toward your personal fluid goal.