In my high school state tournament the other year, it was unbelieveably hot and humid the second day. I was slamming water like crazy, and in that weather you have zero appetite. It ended up catching up with me and I got jittery on the second nine. I'm talking a 16oz bottle of water every other hole here.
One thing to make sure of if you're drinking a ton of water is that you're getting some sort of food in you too. Everything's getting flushed out and leaving you in need of nutrients. And drinking Coke, etc, isn't a good idea either because the sugar will spike your insulin, inevitably leading to a crash a few holes later. Up and down, up and down. From alert to tired.