I used to do the gallon/day thing, but honestly all I did was pee all the time.
I probably drink about a half gallon of water per day in addition to about 64 oz of green tea. I don’t notice anything other than being in the bathroom a lot less.
I got a chuckle out of the thread title…“Is Water Overrated?”, although I know the OP didn’t mean it as such. That’s like saying “Are Carbon-based molecules really necessary?”
It should be obvious that you water intake corresponds to your activity level. For the average bodybuilder I don’t know that hauling around a gallon water jug is entirely necessary, though.
A doctor friend of mine in Canada offered me some simple but valid advice, I think.
1.) Never feel thirsty.
2.) Drink enough that you have 2 “clear pees” a day, preferably spaced several hours apart.