How Much Water Do You Need to Stay Healthy?

It's a rule some people call eight by eight - the idea that you need to drink eight ounces of water, eight times a day to stay healthy. But in an article published today in the American Journal of Physiology, Dr. Heinz Valtin argues there's no medical basis for that belief. Valtin is Professor Emeritus of Physiology at the Dartmouth Medical School. He told NHPR's Trish Anderton nobody knows where the concept of "eight by eight" comes from.