I know lots of people adore it, but I didn't love labouring in water. I liked it during DD's induced birth, but the midwife made me get out after an hour because I was "getting too comfortable" (ha!) and she wanted to hurry the baby out (I had pre-eclampsia).
For the rest of DD's birth I used a hot wheatie bag for pain relief, and it was great. When DS was born I planned to have a water birth. I used the hot wheatie bag again before I got in the tub, and when I finally did I found the water disappointing. It was nice between contractions, but it didn't give me nearly the same level of distracting heat and pressure that I'd got from the wheatie bag - I found it quite wimpy by comparison. So I got out again. I intended to get back in for the actual birth, but changed my mind while climbing in and ended up giving birth standing up in the tub - an over-water birth, if you will!
With my (theoretical) next baby, I'd like to have the tub available, and try standing in it with hot water from a shower head playing on my lower back. If there was really good water pressure I can imagine that being really nice. But who knows? My first two labours were so different - maybe next time I'll find relief by burying my head in the carpet or crawling under the bed or dangling out the window! Labour's weird. It's hard to know beforehand what you'll like. For which reason, I'd recommend keeping your options open - have a tub if it's not too much of a pain to get one, but don't rely on it as your sole pain relief mechanism. (I used hypnobabies with DS, as well as the wheatie bag.)