I wasn't and am not able to have a waterbirth at my local hosptial because of my size, which is fair enough as I understand they have the safety of the MWs and me to consider. (Mind you even if I was under the weight limit no way was my 50kg tiny MW going to have a chance of moving me at the weight limit). But put your mind to how you can still use water in your birth:
Bath at home for as long as you are comfortable - get a bath pillow or two ready as well.
Ask the MW to use a warm compress on your bits during pushingi
Bring stuff to make the shower as comfortable as possible. My MWs suggested 2 squares of foam to kneel on or something foam to rest your head and arms on. And suprisingly, my current MWs are happy for me to even deliver in the shower!
I know it must be frustrating but try to focus your energy on things you can control and change and making this birth as positive as you can!

