Never drink before diving, but have the night before.
How much really depended on what the dive plan was for the next day, and whether I'm on vacation or diving locally NJ.
I also drink tons of water while diving.
Have had a few after diving, but that's usually with dinner, after and hour+ trip back to shore, followed by packing up all the gear. Have had a beer or two from the cooler on the ride back too, but that was after a shallower dive, and also after packing up all my gear.
Last trip I did , I really didn't drink that much, mainly because we were doing a lot of deeper dives, and hauling doubles all over the place at the end of the day. So I was almost falling asleep at dinner even without any alcohol.