Coffee Doesn't Dehydrate You! Why the Myth About Having to Drink a Glass of Water With Your Espresso Is Nonsense

If you’re part of the bodybuilding community, you’ve probably heard this a hundred times: “Want some coffee? Then you have to drink two deci of water with it, or you’ll get dehydrated.” This “gold standard” of fitness advisors and various diet gurus has become such an ingrained mantra that no one questions it.

But science takes a completely different view on this matter. Let’s take a look at why the fear of coffee as the “enemy of hydration” is unfounded and what the truth is about caffeine.

Caffeine Isn’t the Devil—It’s Just a Mild Helper

The idea that coffee acts as a powerful diuretic that flushes all the fluids out of your body is based on very old and incomplete studies. Yes, caffeine has a mild diuretic effect—meaning it stimulates the kidneys to produce more urine. But the catch is that this effect is much weaker than most people think.

A meta-analysis of 16 clinical studies showed that moderate caffeine consumption (up to about 300 mg, which is roughly equivalent to three standard cups of coffee) does not lead to any clinically significant reduction in hydration. That’s because your body is a master at adapting.

Why the “diuretic effect” doesn’t exist in practice

Here’s the main reason why you should stop panicking:

1. Adaptation: If you drink coffee regularly, your body gets used to caffeine within a few days. That initial, slightly increased urge to use the restroom practically disappears for regular consumers.
2. Fluid volume: Coffee is 99% water. Even though the caffeine it contains slightly affects urination, you’re still drinking a volume of water that more than compensates for any additional losses.
3. The research doesn’t lie: Studies using the gold standard—measuring total body water—compared people drinking 4 cups of coffee a day with people drinking 4 cups of plain water. The result? No difference in hydration levels.

What does this mean for your workout?

For a bodybuilder who needs to keep their muscles hydrated for maximum volume and performance, it means one thing: Go ahead and have your coffee.

If you’re not used to caffeine and suddenly down a liter of strong espresso, you might find yourself making more trips to the bathroom. But for 99% of the population who have their cup of coffee in the morning or before a workout, coffee won’t cause dehydration.

Conclusion: Drink water because you’re thirsty, not because of the coffee

Instead of worrying about whether you need to drink an extra glass of water “to make up for it,” focus on your total daily fluid intake.

If you drink water when you’re thirsty and eat plenty of fruits and vegetables, your hydration is perfectly fine. Coffee is just one of many sources of fluids, and thanks to its caffeine, it can also help you focus better and perform better at the gym.

The myth that you need to “balance out” coffee with water belongs in the archives of outdated fitness dogma. Enjoy your coffee and focus on what really matters—your workouts, your diet, and getting enough sleep.