Saw this advertised in this month's Pano:
http://www.crspotless.com/index.php?tpl=

Yes, I hate water spots, Yes I get a lot of them, Yes one of my Pcars is a Garage Queen.

 

There is nothing new with DI water other than it is becoming more and more mobile.

Mr. Clean has the same unit that has been out a while now so it's nothing new and it won't be bad for your car, it's just DI water that is being used as a final spot free rinse. They have the same units at carwashes and coin-op car washes.

We use RO (reverse osmosis) water which is TRUE "rinse and walk away" water.

Anthony

 

I recall someone installing a filter on his water line to remove the minerals.

He completed a DIY with pictures and description of all parts. Do a search... might find something.