Why is water better than Gatorade and soda?

It is not, necessarily. If you are doing high intensity exercise then Gatorade is better for for you because it will give you carbs and electrolytes. If you drink it when you are not doing exercise, then it is bad for you because of its salt content. It will make you very unhealthy. The same goes for drinking too much ater after exercise because you could dilute your salt levels so much that you could die.