Here are common myths about water and hydration, and whether they have any truth behind them.

Brierley Wright, M.S., R.D.
Updated May 17, 2021
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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 leads to 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 really surprised me, especially when it came to myths and truths. Here are five common myths about water and hydration, busted!

Senior woman holding glass of water, close-up
Credit: Getty Images / Maria Fuchs

1. I need 8 glasses of water a day.

Myth. The Institute of Medicine says adult men actually need about 13 cups (3 liters) per day of fluid; adult women need about 9 cups (2.2 liters) of fluid. (You get about an additional 2 1/2 cups of fluid from foods.)

"But one size doesn't fit all," says sports nutrition expert Leslie Bonci, RD, CSSD. Your size and activity level affect your fluid requirements. Simply put, the larger and more active you are, the more you'll need.

"The easiest thing that anybody could do on a daily basis is monitor their urine color," says Douglas Casa, Ph.D., A.T.C., who studies hydration 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."

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.

Check out our article on what to eat before, during and after a workout for more.

2. Coffee and tea dehydrate you.

Myth. While caffeine is technically a diuretic (it increases water excretion from our bodies), you retain most of the water from caffeinated beverages, such as coffee, tea and soft drinks. 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 percent 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 multi-day 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.

Truth. "If someone chooses water in place of calorie-containing beverages, overall calorie intake is less and they may lose weight," says Bonci. A 2010 study in the journal Obesity found that adults who drank two cups of water before a meal ate less at the meal and lost more weight over 12 weeks than the group who didn't drink water before eating.

5. Staying hydrated prevents wrinkles.

Myth. When a person is severely dehydrated, skin is less elastic. This is different than dry skin, which is usually the result of soap, hot water and exposure to dry air. And, no, unfortunately, drinking lots of water won't prevent wrinkles.