Athletes cannot use thirst as a guide for how much water to drink. If fluid needs are not met, athletes become dehydrated and performances suffer. Not replacing lost fluid can lead to a decrease in performance, as well as muscle cramps and other forms of heat illness. Drinking plenty of fluids, especially water and sports drinks, is the single most important thing an athlete can do to improve his or her performance. The color of their urine is the best indicator athletes can use to determine if they are drinking adequate amounts of fluid.
Clear urine means an athlete is drinking enough fluid.
Urine that is yellow in color indicates a need to drink more fluids. Expect yellow urine after a practice session or game, but it should be clear before the next exercise session. Athletes who are not accustomed to drinking prior to exercise will need to acclimate themselves slowly. It may take several weeks for their body to feel comfortable during exercise with this amount of fluid intake. It is also important to drink plenty of fluids.