re: Hardwater spots on automotive glass

Have you tried a steam cleaner?

I bought the one from harbor freight, and other than a couple of the brush attachments not having the steam "hole" bored out all the way when they were poured (which took 2 seconds to fix with a pocket knife to finish punching them out) the thing has been flawless.

It came with a window squeegee attachment that I have used for removal of hard water stains on glass, and along with a terry cloth towel to wipe up, it has worked flawlessly.

I find uses for that steam cleaner every time I get it out for some other task, and so it's not a "one trick pony" either-especially for auto cleaning.