Hi Rob,
I'm using pure water every day now, and it's working great, I don't know anyone else doing it regularly here in the U.K. but a few guys in the U.S. are. I wish I'd done it years ago it would have saved me a fortune in chemicals! Originally I was just looking for an original USP but I was really suprised how well it worked, Have a look on the truckmounters forum and you'll see a pure water rinse thread that goes into a fair bit of detail.
All the best
John