This should be a basic rule! Warm sun will cause waterspots every time. If you do was in the sun work quickly and make sure to dry with an appropriate drying cloth.I have a black Eco and always wash the car before the sun hits my driveway. I am also using unfiltered well water and have never seen a water spot on my car . So I guess the rule is never wash a hot car in the sun and you will be fine. Oh, and drying the car is mandatory!
I can vouche for the Mr. Clean spotless wash as well. Very good product and the filters lasted longer than I expected.A few years back when the Mr. Clean carwash system was introduced, I recall hearing people say that the filter that you used with the "nozzle" really did a good job keeping your car from water spotting when you rinsed it off. I haven't tried it myself; maybe I should give it a whirl.
^^This works well...my "other" hobby of keeping reef aquariums requires the use of de-ionized RO water. I keep a spray bottle of it handy and in the event any spots are evident, a spritz and microfiber does the trick. I wish I could just wash my car with this water, but I only store about 20 gallons, and can only generate about 100 gallons per 24 hours, so that option is off the table.i use somewater on a microfiber towel and it takes them right off, clay bar is a bit extreme for water spots and you should only use it once a year anyway.