Yeah, definitely not epidural during a waterbirth because as mentioned, it numbs you from the waist down and is a pretty major intervention that will require continuous and close monitoring. Possibly gas for pain relief, although one of the benefits of labouring in water is that it provides a great deal of pain relief in and of itself.

I wouldn't recommend sitting on the plug, though. The only thing worse than giving birth on land when you wanted to birth in water, is a poorly-managed waterbirth. Waterbirth is a beautiful experience that is easily spoiled by a frightened, panicked midwife without experience in waterbirth who is desperately trying to get you out of the water. If you are serious about a waterbirth, and your local hospital midwives cannot support you, then you might want to consider looking into a homebirth with an independently practicing midwife, who is experienced in assisting you to have a waterbirth.