Ever heard the saying that "water is a universal solvent"? It really is. It is a fundamental part of our lives, our existence. Our body is about 70% water.
With that large % making up our bodies, how would our bodies function without a contant supply of water? Your thought is as good as mine - the same way a vehicle would function without fuel - it just wouldn't function!
The advantages of taking water have already been mention, but I would say this: NOTHING, I mean NOTHING can take the place of water. Not gatorade, not fruit juice, not soft drinks, not coffee. Why? Simple: Most of them contain substances that are not healthy and these substances counter the positive effects of the added water. And most beverages contain dehydrating agents and this reduce your body's water reserve.
So just remember that water is a universal solvent. Whoever takes it generously keeps moving smoothly, whoever doesn't gradually grinds to a hault.