I had a hospital waterbirth and it was incredible (yes painful, but an amazing experience all the same and I'm sure the water helped).
Remember to drink a lot as the warm water can dehydrate you quicker - I got hubby to offer me a drink of lucozade from a straw every 5 mins or so (that way he can hold it for you). I found music very relaxing too, and had a classical playlist prepared for when I went in.
Also - and this isnt advice for the birth but thought I'd say it anyway - if you are comfortable with it ask the midwife to take a photo of you and baby (+hubby?) when the baby is on your chest in the pool just after the birth. When I look at it my photo still makes me cry as it is the single most incredible and emotional moment of my life. Good luck!