I've been thinking about this...the water around here is really hard. I have a water softener at home, but the outside faucets bypass the softener (lest all that softened water get used up watering the lawn, etc.). At work we have deionizing systems (for supplying spot-free rinse water) that have to be periodically regenerated by the supplier.
I'm sure that companies like Culligan would supply DI (deionization) or RO (reverse osmosis) systems that I could plumb up (inside, in my basement) to my car wash faucet, however that seems pretty nuts...but maybe not to you Autopians. If I just plumbed in my soft water, that would help, not sure if that's a good intermediate solution.
Why do we want DI rinse water again? Is it to prevent spots? Speed drying by not having to get all the drops because they won't spot? Should we get mini-blowers like Bill D and others?