Here are some common beliefs about water and hydration, and whether they have any truth behind them.
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Water is a super-important part of a healthy diet, but many of us are not getting enough in our day-to-day (check out how much water you should be drinking, by the numbers). Staying hydrated can confer a slew of health benefits including keeping your heart and brain healthy, improving skin elasticity, and cooling you down when you exercise. On the other hand, not sipping enough can lead to mental fog, lower energy, overeating and more. But how much water should you really be drinking every day? And does drinking coffee cancel out water-drinking efforts? Some of the answers are truly surprising. Here are five common beliefs about water and hydration, fact-checked!

1. I need 8 cups of water a day.

Mostly True. Water needs vary depending on the person and their circumstances, but the National Academy of Medicine offers a ballpark recommendation of around 11 cups, or 91 ounces, per day for women.

That said, we meet up to 30% of our fluid needs through food (think: fruits, veggies, soups, etc.), so the net amount needed through drinks is around 8 cups per day.

If you spend more than an hour exercising continuously, or live in a hot climate, you may need to chug more water than the standard 8-a-day. "The easiest thing that anybody could do on a daily basis is monitor their urine color," says Douglas Casa, Ph.D., a hydration researcher at the University of Connecticut. "Lighter urine color, like lemonade, means you're generally well-hydrated. If it's darker, like apple juice, you are most likely dehydrated."

Data from the large National Health and Nutrition Examination Survey shows that most people are adequately hydrated, yet they're largely meeting their fluid needs through foods and drinks other than water, like coffee, tea, soda, fruit, veggies and even pasta, bread and meat.

Older adults' fluid needs don't change, but they're more likely to become dehydrated because their sense of thirst declines. Pregnant women and nursing mothers need slightly more water. Some medications, such as antihistamines and certain antidepressants, increase your fluid needs too.

While any beverage will help you meet your fluid needs, sugar- and calorie-free water is the ideal choice. But, if plain H20 feels blah, liven it up with a slice of lemon (or other fruit), cucumber or some herbs (like mint).

2. Coffee and tea dehydrate you.

Myth. Latte lovers, you're in luck! While it's been widely suggested that coffee, tea and other caffeinated drinks are dehydrating, that's simply not the case. In fact, there's plenty scientific proof dating back decades. A 2003 study published in Journal of Human Nutrition and Dietetics found no support for the notion that normal caffeine consumption—around 250 to 300 milligrams per day for healthy people, or the amount in two or three cups of coffee or five to eight cups of tea—is associated with poor hydration status. Fast-forward to a 2014 study in the journal PLOS One; the authors titled their study: "No Evidence of Dehydration with Moderate Daily Coffee Intake."

This urban legend persists because caffeine has a diuretic effect—meaning it stimulates you to pee. But coffee and other caffeinated drinks also contain liquid, so you end up with more fluid than you lost.

Alcohol, on the other hand, particularly at high doses, can cause you to excrete more than you consume. One drink, especially of beer, won't do much (it's about 92% water), but wine and hard liquor have more of a dehydrating effect because of their higher alcohol content.

3. The more water, the better.

Myth. It is possible to overdo it. Water intoxication, or hyponatremia, a serious condition when blood sodium levels drop precipitously, can be caused by sweating excessively over several hours and drinking way too much water (versus a sports drink) while not eating or urinating (which often slows during intense physical activity). This could happen to someone who engages in a long athletic event (e.g., a marathon or multiday hike). Symptoms include confusion, disorientation, weakness and nausea. Hyponatremia can lead to seizures, coma and death without prompt medical attention.

4. Drinking water can help me slim down.

Mostly myth. Gulping a glass of water may help you take the edge off of hunger, so think of those sips as a smart strategy when you're distracted by a growling belly and your next meal is a ways away.

However, the practice of drinking lots of water before a meal is unlikely to influence what you eat, so you'll eat the same amount regardless of whether you slurped down some water. Results from a 2019 study published in the journal Physiology Behavior revealed that when people drank up to 2 liters of H20 throughout the morning before a buffet lunch, the ones who were normal weight ate a bit less while those classified as overweight or obese ate the same amount. So for most people, preloading on water may help you get through the day a little less hangry, but likely isn't going to do much to modify your eating habits.

5. Dehydration can make you sluggish.

True. Coffee might be the first thing you think of when you're feeling tired, but good ol' water may be a better pick-me-up than caffeine. Numerous studies suggest that being parched can result in higher levels of fatigue and lower levels of alertness and mood. Every cell in your body requires fluid in order to function at peak performance. When they don't get enough, even the ability to produce cellular energy gets impacted, which can manifest as fatigue. Beyond that, your heart rate may become elevated to maintain healthy blood pressure levels. This, again, requires extra effort.

To encourage your water intake, park a water bottle on your desk in the morning and try to finish it by midday. Then, refill and repeat. And have a glass of water at each of your meals. Feeling better yet?

Bottom Line

Drinking water and staying hydrated is good for your mood, energy levels and cognition. In general, you should aim for 8 cups of water per day and fill up on water-rich foods, such as fruits and vegetables. Doing the "pee test," or looking for urine that looks like lemonade in color, is a good way to gauge if you're properly hydrated.