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How Much Water Should You Actually Be Drinking a Day? Here's What Science Says

  • Writer: Benjamin Payson
    Benjamin Payson
  • Apr 30
  • 3 min read


We’ve all heard the advice—“Drink eight glasses of water a day.” It’s a piece of wellness wisdom that’s been repeated for decades, but how accurate is it really? As it turns out, the story is a bit more complex—and a lot more interesting—than just counting cups.

Let’s break down what the science actually says about hydration, how much water you need, and whether it’s possible to drink too much.


Why Water Matters More Than You Think

Water isn't just something you drink when you're thirsty—it’s essential to nearly every function in your body. From regulating your temperature and delivering nutrients to flushing out waste and lubricating your joints, water is the MVP of human biology. Even mild dehydration (we're talking as little as 1–2% body weight loss through fluids) can lead to fatigue, headaches, mood swings, and impaired cognitive performance.

And if you're physically active, living at altitude, spending time in a sauna, or just out in the heat? Your hydration needs go up significantly.


So, How Much Water Do You Really Need?

There’s no universal “one-size-fits-all” number—but we do have science-backed guidelines. According to the National Academies of Sciences, Engineering, and Medicine, the average adult needs:

  • 3.7 liters (125 ounces) per day for men

  • 2.7 liters (91 ounces) per day for women

Now, before you start panic-chugging water bottles, remember that this total intake includes all fluids—not just plain water. It also includes moisture from food, which typically makes up about 20% of your daily fluid intake. Think of fruits, vegetables, soups, smoothies—those all count toward your hydration.

Coffee and tea? Also yes. While caffeine is a mild diuretic, research shows that moderate consumption of caffeinated beverages doesn't dehydrate you. Even sparkling water, milk, and electrolyte drinks help meet your needs, as long as they’re not loaded with sugar or sodium.



When Should You Drink More?

Your baseline needs might rise depending on your activity level, diet, and environment. If you’re working out, sweating, eating a high-protein or high-sodium diet, or dealing with heat and humidity, you’ll need more fluids. Pregnant or breastfeeding? You’ll need to increase your intake to support your baby and milk production. Feeling under the weather? Vomiting, diarrhea, or fever can rapidly dehydrate you.

But the simplest guide? Pay attention to your body. Thirst is a great start, but it’s not always timely—by the time you're thirsty, you're already on your way to dehydration. A more reliable cue is your urine: pale yellow means you're in the hydration sweet spot, while darker amber can signal you’re falling behind.





Wait—Can You Overhydrate?

Absolutely. While dehydration gets most of the press, overhydration, or hyponatremia, is a real (and sometimes dangerous) condition.

Hyponatremia happens when you drink so much water that it dilutes the sodium levels in your blood. This causes your cells to swell, which can lead to nausea, confusion, seizures, and in extreme cases, even death. It’s rare—but it does happen, especially among endurance athletes who drink excessively without replacing electrolytes lost through sweat.

A famous example comes from marathon runners and ultradistance athletes who, in an attempt to stay ahead of dehydration, end up consuming far more fluid than their bodies can excrete. This can throw the body’s delicate fluid balance into chaos.

To avoid this, balance your water intake with your electrolyte needs, especially during prolonged activity. Don’t guzzle gallons of water just because you think you should. Drink consistently throughout the day, and if you’re sweating a lot, consider drinks with sodium and potassium to help keep things in balance.





The Bottom Line: Listen to Your Body, Not a Rule

The “eight glasses a day” rule is a good starting point—but it’s not gospel. Your real water needs depend on a combination of personal and environmental factors, and the best approach is to stay aware of how your body feels. Are you thirsty? Is your urine light yellow? Are you performing well mentally and physically?

Then you’re probably doing just fine.

And if you're unsure, aim for around 2.7 liters (women) or 3.7 liters (men) daily from all sources, and adjust as needed. Hydration isn’t a competition—it’s a habit. So sip smarter, not harder.





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