I have a spray bottle of Z6 in the trunk, like my brethern. I also have a Z7 solution (using distilled water) in a spray bottle. And, a bottle of straight distilled water.
Yesterday, I parked on the street next to a business that has the unbelieveble and inconsiderate practice of turning on their sprinklers twice a day, during the day time. Huge water spots when I got back to the car. The Z6 would not take them out completely. The Z7 did. Then, I sprayed the distilled water on, and wiped, to get the Z7 off.