The point of water is to bring relaxation and support and create a calm nurturing and familiar environment for baby to enter the world. There shouldn't be a pressure to push push push, but to breathe the baby down and allow the body to do all of the work, however gradual it might be. As the baby crowns and recedes back inside, tissues are oxygenated and can stretch just a bit further the next time a contraction comes. Water can do so much if your attitude is confident and your medical support doesn't micro-manage.
I tried the water birth with my second daughter... I am now pregnant with my 4th and I didn't have any luck with it helping mine lol but everyone is different if you want to try it I say go for it it is a different experience and it might help you a ton!!!