Gatorade contains glucose which can provide energy and replenish electrolytes lost through sweat. In general however, the sugars and harmful additives in it are not only bad for you, they are also an unnecessary way of restoring hydration. Water is just as good so not only does it provide good hydration, but good health as well. To answer your question more specifically however in reference to only hydration, both would have the same effect. However, Gatorade is usually consumed during physical activity, not hot days so water is safer and a more refreshing way to beat the heat.