I once had a black Vette that I left parked next to some under ground sprinklers. The water got all over the car and then the sun dried it. I couldn't get it off with any thing I tried. Whats crazy is that finally I brought the car to a car wash and used a power sprayer and hit it with a good close range blast which took the spots right out with out messing up the paint!.....Although I would not recomend this with an original paint car....
