For all the reasons above and the fact that we're made up of, what, 70% water or something like that, probably has something to do with how helpful being in water to birth is!
My two birth stories talk a bit about the role of the birth pool - the last one won't be hard to find, the one for DS will be back in 2007 (I'm pretty sure...it was a while before I got round to writing it!).
By the time you're getting to the baby expulsion bit and other bits come out you have ZERO care factor and it all gets cleaned up by midwives before you can even notice it anyway...but your partner will tell you, if he's game!!
Really, I could think of nothing more blissful than birthing in water, so that's what I went for both times.
And, lady, if you've got an Ob who wants you to do this, GO FOR IT!! And then, tell us all about the service you get from him and plug him widely - there are so few of his type around!
I'm so glad you have a fantastic caregiver