First time mummy - I think it's so great you're looking into a waterbirth.

My first was a waterbirth (Angliss Family Birthing Centre, brilliant amazing resource), and it was wonderful in terms of pain management and focus and relaxation between contractions.

My second birth, I thought, it'll be fine as long as I can find a bath - I was hanging for a second waterbirth! I didn't make it to the hospital though, and had bub on all fours with my shower falling on my back. That was fine. So be encouraged a bit, that if you decide not to pursue the home water birth option (worth looking into), there are still ways to birth using water as pain relief/relaxation.
It might be worth asking if the hospital will let you push while under the shower - as Melissa says, you may not be inclined to move anyway at that stage, but ideally you'd have someone supporting you in that stage and not turning off the water and trying to move you.

I'm pretty sure the only option available to me during my waterbirth would have been gas. I assume on a low setting. It never occurred to me to ask for drugs though in the waterbirth (and there was no option for that at home ), I was taken by surprise by how efficient my birth hormones were in terms of helping me labour and focus and birth. Really amazing.

All the best as you continue to figure out your options! xo