10 Complete Falsehoods About Food

You Need Eight Glasses of Water a Day
Eight glasses of water is way more than the average person needs in a day. iStockphoto/Thinkstock

If you don't drink eight glasses of water a day, you'll struggle under the weight of dehydration, a malady that causes everything from mental confusion to joint pain to facial wrinkles, or so the conventional wisdom goes. The "eight glasses of water a day" adage is such widespread advice, it holds a spot between "eat your vegetables" and "you need eight hours of sleep a night."

But is chugging eight glasses of water a day really good advice? It all depends on your activity level and age, and the climate where you live. Truth is, "eight glasses of water a day" isn't a hard-and-fast guideline for minimum hydration. Current research contends you only need half that amount, about 32 ounces (about 1 liter), to stay hydrated. What you really need to focus on is whether you are replacing the fluids you lose through sweating and urinating. For example, if you spend your lunch breaks running a 5K instead of sitting at your desk, you'll need to drink more water throughout the day.

Plus, you don't necessarily need water to replenish your body. Juice and milk are two options. Even coffee, tea and soft drinks -- long believed to have a dehydrating effect on the body because of the caffeine they contain -- are about two-thirds retained by the body and contribute to daily liquid intake.

Even if you skipped liquids entirely for a day, you'd probably still be OK: Studies show most Americans derive about 32 ounces of water from solid foods [source: Mikkelson Bellenir].