A surprising look at the benefits of water and how much you actually need.
Credit: David Muir/Masterfile

During the dog days of summer, we're all reaching for a cool glass of something. Should that always be water, and how much do you really need? The questions are answered in Eat Up, Drink Up, which illustrates how food―along with all manner of beverages, from coffee to wine to water, of course―is a great source of the fluid your body needs.

Experts have known for a while that the eight-cups-of-water-a-day "rule" isn't true, and the average healthy person can use thirst as a guide to how much fluid to drink. But the myth still holds sway. So Dan Negoianu, MD, and Stanley Goldfarb, MD, of the University of Pennsylvania reviewed the research pertaining to water consumption and published their findings in the Journal of the American Society of Nephrology. No one knows how the 64-ounces-a-day advice originated. "There is no single study―and therefore no single outcome―that has led to these recommendations," they note. They also dispelled other myths about water consumption:

• Water flushes toxins from the kidneys. Little is known about what type of toxins are cleared by the kidneys, so it's difficult to determine what, if any, benefit comes from drinking lots of water.

• Drinking water helps with weight management. No studies demonstrate that "drinking a large volume of fluid over the course of a day will decrease the number of ingested calories."

• Drinking water improves skin tone. While someone who is truly dehydrated won't have great-looking skin, there is no evidence that consuming large amounts of water has an effect on the skin of otherwise healthy people.

Nonetheless, water plays a central role in our bodies' function, and when you're thirsty, take heed. Sip your favorite beverage, or enjoy a fluid-rich dish like Heirloom Tomato Salad with Tomato Granita .