I've been in water with all three but not delivered in it although I wanted to, it just never felt right at the time.
First one it was bliss, got in around 2 hours after I hit 4cm, later progressed to gas and air in pool. Got out because nothing was happening at the end and they wanted to have a look, but in hindsight with two more births behind me, that's just how my pushing stages go.
With second, appalling, got in much too early because of the amazing memory of the first one and it did nothing at all. Got out and asked for an epidural instead.
With third, relied much more on calming/distracting/pacing self techniques for the earlier part, got in just as I was starting to really struggle to cope and it was bliss again. Just solid relief. That allowed me a couple of hours of very deep inner relaxation to cope with each contraction until I wanted gas and air to be told I had to get out! (This is not UK) decided I wanted the gas more than I feared getting out of the water so got out. It was fine.
Well worth it as long as you use in conjunction with other coping strategies! In UK they won't let you get in too early so won't have the issue I had with my second.