Anyone wash their coach with a deionized wash system?

I forgot to mention, while visiting my brother in law in the Midwest I wanted to wash my truck but the water there is so bad I only did it once (took me forever to get rid of the hardness streaks). He then pulled out a spray bottle made by ? (turtle wax, McGuire's or similar). I sprayed this stuff on the vehicle and dry towel as I dried. I was amazed how it worked as there was no water hardness marks when done drying.