General Guidelines:

• Monitor fluid losses- weigh in before and after practice, especially during hot weather and the conditioning phase of the season.
• Do not restrict fluids before, during, or after the event.
• Do not rely on thirst as an indicator of fluid losses,
• Drink Early and at regular intervals throughout the activity.
• Do not consume alcohol before, during, or after exercise since it may act as a diuretic and prevent adequate fluid replenishment.
• Discourage caffeinated beverages a few hours before and after physical activity because of their diuretic effect. (oooops I tend to do this a lot) 

Before Exercise: Drink about 400 to 600 ml ( 14-22 oz) of water or sports drink ( approx. 17 oz), 2-3 hours before the start of exercise.

During Exercise: Drink 150-350 ml (6-12 oz) of fluid every 15-20 mins, depending on race speed, environmental conditions, and tolerance; no more than 1 cup (8-10 oz) every 15-20 mins.

After Exercise: 

• Drink 25% to 50% more than existing weight loss to ensure hydration 4-6 hours after exercise.
• Drink 450-675 ml (16-24 oz) of fluid for every pound of body weight lost during exercise.
• If an athlete is participating in multiple workouts in 1 day. then 80% of fluid loss must be replaced before the next workout.

Source: Murray R: Fluid,electrolytes, and exercise. In Danford M, editor: Sports nutrition: a practice manual for professionals, ed 4, Washington, DC, 2006, American Dietetic Association.