Nothing will deplete your physical and mental performance faster than dehydration. Along with all the other fluids you take in throughout the day (milk, juice, coffee, tea…), drink at least 40-80 ounces of water. Research shows that people who drink at least this amount of water each day, versus those who drink 16 ounces or less, have a significantly less risk of healthy issues including cancer. Be in the habit of drinking 16 ounces of fluid before exercise. After exercise, replace each pound you lose by sweating with 20-24 ounces of fluid.
-Goucher, Kara, and Adam Bean. Funning For Women. 1st ed. New York: Simon & Schuster, 2011. Print. Touchstone.