That is it, just use DI water. No spots, period. No need to even dry, no spots, period.
really...

 

DI - distilled water ? Please explain - very intrigued when you say "no drying"

 

I am not the water expert, so bear with me here. DI = DeIonized. The "tap" water is run through a "media" that removes impurities, minerals, etc. (Reverse osmosis filtration does a similar job.) I understand that you could use distilled water, but I don't know how to make that work in a practical manner. I am told that even "soft water" leaves residue behind if you do not dry the car soon enough.

Water spots I used to get were the result of impurities being left behind after the water evaporates. If there are no impurities to leave behind, no "spots".

I lease a "tank" from IONICS (10" dia x about 48" tall) that I connect the hose and pressure washer to (set at low pressure for car). They come out and replace it when needed. Costs about $12.50 per month and $42 to swap out).

Although I still dry my cars, I don't need to expend any effort or rush to dry them. Sometimes hours may go by before I get to it.
Really, the best thing I ever did to make car washing easier at home.

 

Since i have reagent grade water available to me, i have always thought about giving this a try, but in my situation it would be difficult to "rig" a spigot to use. I have to say that I am still curious to try it though.