Myth #8: You need eight cups of water each day to be healthy.
Truth: Most places and doctors recommend that adults drink eight cups of water each day, but you might be surprised to know that there is no scientific evidence that everyone needs eight cups. In fact, most experts aren't even sure exactly where that recommendation came from. One source of this "myth" may be a 1945 article from the National Research Council, which noted that a "suitable allowance" of water for adults is 2.5 liters a day. Most of the water you need each day comes from the foods you eat, but there are still many benefits to drinking this much water.
Myself: DRINK MORE THEN 8 CUPS OF WATER! Ok, so on The Biggest Loser I have found that they do not have the contestants drink more then 8 cups each day to avoid water retention. In a long term weight loss keeping yourself hydrated is more important then the weigh in. I attempt to drink as much as I can in order not to become dehydrated.