Why do I have to drink so much water?
To rehydrate during exercise, they recommend 7-10 oz every 10-20 minutes, depending on the individual's sweat rate and climate. Rehydrating immediately after exercise is also important to aid recovery. For every pound lost during exercise, the individual should consume ~17-20 oz of fluid afterwards.
Other fluids than water that include carbohydrates and electrolytes, such as Gatorade, are very good at hydrating exercising athletes. Carbohydrates help speed up the hydration process and electrolytes that are lost in sweat need to be replenished.
Exercising in the heat and not being adequately hydrated can quickly lead to muscle cramps, heat exhaustion, and heat stroke.