I have really hard water and have a CR Spotless unit too. I wash inside or later in the evening to avoid the sun. I rinse the truck of with the regular water, then use the foam cannon or gun. I wash then rinse with the regular water then rinse the car with the deionized water.
I dry using the Master Blaster. If I see any water spots after drying I use detail spray and a waterless wash towel.