It isn't necessarily better. But unlike water, it has carbohydrates and electrolytes. Carbs are fuel for your body to burn, while electrolytes are ions that allow your body to transmit electrical signals and your cells to generally function properly. As athletes sweat they lose electrolytes and water while also burning calories. Gatorade replenishes all three of these. But keep in mind water is the most important part. Eating a healthy meal some hours prior to exercise, will ensure that your body is in better balance. Sports drinks are really only necessary when athletes are doing extended periods of strenuous exercise.

When athletes sweat, they lose both water and electrolytes - mainly salt. The body needs an appropriate concentration of salt in its fluids. Gatorade matches that concentration perfectly, being about as salty as blood. As a result, for someone who is losing both water and salt, gatorade is an effective way to replenish both, as well as provide other useful things for athletes (sugar = fuel) as well.