Half water, half vinegar. If it doesn't work use straight vinegar. If your windows are newer such as Pella windows it only calls for vinegar or vinegar water nothing that contains ammonia. I am not sure but probably because of the protective coating. If you have hard water that also could causing the problem. Let me know if this helps if it doesn't give me the brand of it product and let me see if I can find a solution for you.
The water spots are caused by hard water drying on the glass. From washing car or from lawn sprinklers. Vinegar will or should do the trick. You must have a cool day when doing this and spend some time wetting and cleaning. Do not use any sort of abrasive type of cleaning pad other than a plastic scrubbing pad used for cleaning coated pans. Anything else will cause the glass to become scratched.
Saturate papertowel and place all over the windshield. (do it in a shaded area) Leave for a while and then wipe off.
Thank you for the suggestions but this doesn't answer my question becauseit doesn't work.
Rainex works well for me...gets most off & if you keep it up every 3months or so, you won't get any new ones. :)