Here’s the recommendations from the American College of Sports Medicine:
- Drink roughly 2 to 3 cups (0.5 to 0.7 liters) of water during the two to three hours before your workout.
- 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.
- 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.
Water is the best fluid to replace lost fluids if you’re exercising less than 60 minutes. If you’re doing intensive exercise for more than 60 minutes, you can use a sports drink which contains carbohydrates and electrolytes.