Hi, Nick...
Permanent Publications in the UK has a stash of our
books that would likely be helpful (they have 5th edition create an oasis, not 6th, but the 5th
should work for you. Perhaps in their network they could connect you to someone who could help you with
permaculture plumbing? The book should do a decent job of guiding you to a system appropriate to your climate, and/or help you evaluate the merit of suggestions from
local practitioners.
Good luck!
Art