To stay well-hydrated for exercise, the American College of Sports Medicine recommends that you drink roughly 2 to 3 cups (0.5 to 0.7 liters) of water during the two to three hours before your workout. Also, drink about 1/2 to 1 cup (0.12 to 0.23 liters) of water every 15 to 20 minutes during your workout. You may need more the larger your body is or the warmer the weather is. Finally, drink roughly 2 to 3 cups (0.5 to 0.7 liters) of water after your workout for every pound (0.5 kilogram) of weight you lose during the workout.