The Rumor: You must drink eight glasses of water a day

We’ve all heard it before: To have perfect health and perfect pores, you need a die-hard dedication to drinking water. In fact, everyone from our doctors to our favorite preachy fitness magazines says we need to down eight glasses a day.

But is it true? And will any liquid (like, Diet Coke or your favorite shade of Vitamin Water) fill the bill? To find out, we turned to Dr. D.J. Verret, MD, FACS, and the host of the "Medical Myth Minute" radio show, a syndicated radio segment devoted to debunking medical myths.

The Verdict: Any drink will do

"Our bodies are 80 percent water," says Dr. Verret. "If you don’t eat for a week, it’s not that big of a deal. But if you don’t drink for 24 hours, you could be in significant trouble. You need to replace the amount of water you lose each day." (He's referring to the fluids we lose to breathing, sweating, urine and bowel movements each day.) For years, doctors have waffled on whether or not it's necessary for everyone to drink eight glasses a day. In reality, the amount you need may vary, depending on your gender and lifestyle.

The Institute of Medicine found that the average healthy human female in a temperate climate (i.e., not within walking distance of a tiki bar) requires 2.2 liters of fluid per day; for men it's about 3 liters. "Eight glasses is about two liters, so that’s pretty close to the recommendation," notes Dr. Verret.

But it turns out you needn’t chug Poland Spring as if your life depended on it: "Eighty percent of fluid comes from drinks like water and sodas, and 20 percent comes from the foods we eat," explains Dr. Verret. In other words, even your Diet Coke habit does its part to rehydrate you.

Another thing to consider: Fruits and veggies have a very high water content. Your average strawberry is 92 percent water. Tomatoes and cucumbers are worth their weight in liquid as well. And, of course, water itself is calorie-free, inexpensive, pure and plentiful.

But beyond these baselines, there are situations, says Dr. Verret, that may merit a closer look at your fluid intake:

You work out regularly. In general, you need to down an extra 1.5 to 2.5 cups of water to compensate for a short bout of exercise -- more if you suddenly make good on that threat to hit power yoga three times a week. Hate the taste of H2O? Consider a sports drink like Gatorade -- it won’t rehydrate you any faster, but it will replace salts and other minerals lost through sweat, rebalancing your electrolytes.

You live in Tahiti or Tahoe. Heat makes you sweat. Whether you’re lucky enough to live on a tropical island or just visit one, you’ll need to work harder to stay hydrated. Similarly, your skin and mucous membranes can dry out in low-humidity environments, says Dr. Verret, so more fluids should be on the menu.

You’ve been sick. If you get the flu, you’re vomiting a lot or you have diarrhea, you can easily wind up with a fluid deficit. "You’re not eating well, you’re not taking in liquids, and at the same time you’re losing a lot," says Dr. Verret. Just keep sipping is the rule here.

Your middle name is Merlot. "Alcohol and salted nuts are a deadly combo out at the bar," says Dr. Verret. The reason? Alcohol dehydrates, and nuts contain only trace amounts of liquid. Instead, when out drinking, opt for one-part water to one-part alcohol, which is good for your hydration and your hangover.

You just had (or are expecting) a baby. Women who are expecting or breastfeeding need to seriously increase their liquid intake in order to stay hydrated. In fact, the Institute of Medicine recommends that pregnant women drink about 10 cups of fluid daily and breastfeeding moms drink about 13 cups.

Some tips for staying hydrated yourself:

1. BYOB(ottle). You’re a lot more likely to drink up if you carry your liquid of choice with you. Whether taking it to work or your workout, get a cute, portable water bottle and keep your favorite beverage close at hand.

2. Check your pee. It may not be pretty, but it's the fastest, science-approved way to make sure you’re getting enough fluids. Ideally, you’re looking for urine that’s a pale yellow color. If it’s yellow and concentrated, it’s time to get hydrating.


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