Where I work, it often rains in the morning and then clears up to a hot and sunny afternoon. I've had that leave pretty stubborn water spots that I mostly notice on the glass. So far I haven't really noticed them lasting past the next wash on my paint. But for the spots on glass, I noticed that vinegar and AIO did nothing. I did have some hard water spotting that came off with vinegar.
I just assumed that the rain water contains some salts since I live in an area where you are constantly exposed to sea air. Growing up and now again living in Hawaii, I've always noticed glass spotting, especially the wiper pattern type on front windshields. When I lived in Washington, my glass didn't have water spotting, just tons of tiny pits from driving on gravelly and sandy roads :furious: .