Hi Kevscar,
I found some abstracts in PubMed that may be helpful to you. I just used the search term - Aquagenic Urticaria - . It really might be helpful for you to check them out.

Some were regarding antihistamines and one other I found mentioned using a barrier cream. Yet another mentioned that it could be made worse by heat or cold. Also mentioned was Aquagenic pruritis as differential diagnosis.

Anyway, I just wanted to mention this, so don't give up searching for treatments.