Age-old stories and advice would have us believe drinking a gallon of water a day will solve every problem we have, from weight loss to anti-aging. But is it a myth? I can't imagine it would help much more than the frequency of my trips to the bathroom. So before trying it myself and subsequently carrying a gallon of water around with me all day, I decided to ask experts in fitness, nutrition, and skin what that water would really affect. Turns out it's not a cure-all for any and every body-related issue. But there are a few surprising things that added hydration helps with.