Do I really need to drink eight glasses of water per day?

We hear it all the time: We should drink eight 8-ounce glasses of water per day. But is this fact or fiction?

There are no good scientific studies to support the eight-by-eight rule. The origins of this recommendation date back to 1945. The original guidelines actually came from a misinterpretation of a recommendation from the Food and Nutrition Board. The recommendation stated that a person should have 1 ml (about 1/5 of a teaspoon) of water for each calorie he or she consumes. The average diet at the time was approximately 1900 calories, meaning you needed about 64 ounces of water per day.

Now the Institute of Medicine sets general guidelines for total water intake. It recommends that women consume a total of 91 ounces (that's about 2.7 liters) per day -- from all food and beverages combined. For men, it's about 125 ounces a day (or 3.7 liters). Depending on your diet, about 25% of the water you consume comes from your food.

Everyone knows that drinking 8 glasses of water a day is critical to good health -- or is it? In this video, Harvard Medical School's Dr. Julie Silver reveals how much water you really need and the surprising sources of water in your diet.