How Much Water For Exercise?

From: The First 20 Minutes: Surprising Science Reveals How We Can Exercise Better, Train Smarter, Live Longer by Gretchen Reynolds

"So how much and what should you drink if you regularly exercise? 'That's what we'd all like to know,' Dr. Coyle says....

"The most widely accepted DIY method of deciding if you're drinking properly is 'to weigh yourself before and after a workout or race,' Dr. Coyle says.

"So weigh yourself before your next hour-long run, bike ride, or other exercise session, preferably without your shoes or shirt on. Drink as you normally do. Weigh yourself again at its conclusion. 'If you're not losing more than two pounds of body weight in the course of an hour due to sweating,' Dr. Coyle says, 'you're fine. Don't change anything. If you are losing more than two pounds in the course of an hour, you may need to drink more.' And if, as happens rarely, you actually gain weight, cut back dramatically on how much drink in subsequent sessions. Weight gain during exercise is the primary symptom of hyponatremia (which, perhaps thankfully, is very uncommon in exercise lasting less than three or four hours and conducted at a slow pace)."

Note:

Dr. Edward Coyle  Ph.D., is an exercise physiologist at the University of Texas at Austin who's studied this topic for decades and served for many years as a consultant to cyclist Lance Armstrong