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The Eight Glasses of Water a Day Thing Is Bullshit

Surprise! It was originally a marketing ploy by the bottled water industry

Americans don’t drink enough water. That’s a fact: A study conducted by the U.S. Centers for Disease Control and Prevention found that 43 percent of American adults drink less than four cups of water a day, and this figure includes 7 percent who drink no water at all (literally, none).

But how much do we need to drink?

You’ve probably heard that you’re supposed to drink eight 8-ounce glasses of water a day. It turns out, however, that’s actually a bunch of crap. The myth is believed to have originated with a 1945 Food and Nutrition Board recommendation that claimed we need about 2.5 liters (or 84 ounces) of water per day. While this is actually a good number for most people — nutritionist Carolyn Dean suggests consuming half the number of pounds you weigh in ounces of water each day (i.e., you should consume 75 ounces if you weigh 150 pounds) — it’s also very misleading.

When the bottled-water industry seized on the figure to boost sales, they conveniently ignored the vital sentence that closely followed the claim: “Most of this quantity is contained in prepared foods.”

That’s right — you can stay plenty hydrated by simply eating plenty of water-laden fruits and vegetables as part of your diet. Watermelon and strawberries, for instance, are about 92 percent water, and zucchini, radish and celery are about 95 percent water.

Despite all of those hydrating fruits and vegetables, the perpetuation of the drink-even-more-water myth is still going strong. You can see it in the advice of the National Hydration Council, an organization put together by Danone, Nestlé and Coca-Cola with the sole purpose of promoting the virtues of their bottled water over sugary soft drinks (which, ironically, they also sell); the claims of stars like Jennifer Aniston (who is a brand ambassador for Smart Water) that their “beauty secret” is drinking several liters of water a day; and magazines recommending we drink two or three liters of water a day for “glowing” skin. (It definitely works: Bottled water sales continue to rise.)

Contrary to these stories, however, there’s no real scientific proof that, for otherwise healthy people, forcing yourself to drink more water than you feel like (that is, more than you naturally drink to quench your thirst) has any benefit whatsoever. Numerous studies have failed to find benefits in kidney function or all-cause mortality from increasing fluid intake. Other reviews have similarly failed to find any evidence that drinking excess water keeps the skin hydrated and wrinkle-free.

And so, the question remains: If we don’t really need to drink eight glasses of water a day, how much do we need to drink? In general, the CDC says there’s no need to worry about dehydration as long as water is your main choice of drink, both when you’re feeling thirsty and when you’re drinking with a meal. They add that you might need to drink more water if you’re physically active, running a fever or in a hot climate.

How much water you need to drink also depends on how much hydration you get from other sources, like water-rich foods or non-water beverages (while Diet Coke, for instance, does count toward your daily water intake, it also contains additives like sodium and caffeine that can potentially dehydrate you if you’re sensitive to caffeine). Sharad Paul, author of The Genetics of Health, puts it simply: “The best guide for staying hydrated is drinking water when your body asks for it.” Recent research found that it becomes more difficult to swallow water when you’re already hydrated, so more specifically, listen to your throat.

Another simple way to ensure you’re drinking enough water is to keep an eye on the color of your urine: Urine gets its color from a pigment called urochrome. When you’re dehydrated, this pigment won’t be diluted, so your urine will appear darker. Paul adds, however, that this method isn’t foolproof: “Your pee may not be clear for many reasons — like, if you have a certain diet [beetroots, for example, can apparently darken your urine] or take certain supplements [high levels of vitamins B and C can also color your urine].” Dean adds that crystal-clear pee might also be a sign you’re drinking too much water: “Actually, clear urine may mean you’re drinking too much water, and therefore, you’re losing essential minerals like magnesium — lighter shades of yellow (rather than totally clear) tend to show that you’re properly hydrated.”

What it all boils down to is that there is no formal recommendation for how much water you should drink every day. Instead, it’s a matter of common sense: If your throat doesn’t feel like hot, sand-blasted asphalt, chances are, you don’t need to chug that pitcher of ice water right away. And while you can technically replace water with, say, Diet Coke, you’re not doing your body any favors. So you don’t have to drink eight glasses of water a day, but commons sense suggests you should at least drink a few.