Drinking to Drunken Can Be a Good Feedback Mechanism

Drinking to thirst can be the plan and thirst is a good feedback mechanism. For ultra-endurance athletes, body weight loss doesn't necessarily reflect fluid loss. It's pretty good for the first sort of three or four hours of exercise but once you're exercising for 10 or 15 hours, you have other causes of weight gain and weight loss that are not related to water.