I'm in Canada so I don't know if it's different here but I'm doing a home water birth and went with a midwife just because I've heard awesome things about them and preferred a midwife over a doctor, that was always my plan. But I agree with Mrscrow first step would be talking to your doctor.
I am planning on having one here as soon as this little lump decides to enter the world. Im really excited about mine but I cant say anything about it yet, but ill let you know later. You need to ask your OB if he/she will do one and if your hospital has a tub. If not and you are serious about one, you may need to find a new OB and look into a birthing center or a place that rents out tubs for a home birth. The first step is talking to your doctor.