for mineral water spots, look for a glass polish instead of glass cleaner. I've had good luck with a Griot's product:
https://www.griotsgarage.com/product/fine+glass+polish+16+ounces.do?sortby=ourPicks&from=Search
So I tried this from Amazon (cause I'm cheap and it came with, what actually worked out as a really good sponge for polishing)
Amazon.com: Invisible Glass 91411 3.38-Ounce Glass Stripper Water Spot Remover Kit Eliminates Coatings, Water Spots, Waxes, Oils and More to Polish and Restore Automotive Glass: Automotive
www.amazon.com
I was surprised that it seemed to work pretty well on the mirror. I still have to test it out in a high humidity/rain situation where the water stains really showed through but it seemed to work so far. I can only surmise that the polishing components of the glass polish are much harder/larger than that of paint polish since rubbing compound and polish didn't put a dent in it. That being said, the passenger side of my truck was covered front to back with water stains that wouldn't come out when I had it detailed, when I first bought it. (The previous owner parked next to his condo sprinkler system and between the black paint and sun, really baked them in). I ended up polishing the whole side of the truck by hand seeing as the detailer I had wouldn't do more than a light polish with a machine because of his fear that in chasing the water stains he would burn the paint. I noticed the water stains on the passenger side glass (oddly not on the passenger mirror) and tried polishing compound on the glass, to no avail.
I tried the glass polish on the passenger windows and after about half the bottle and 30 min, got about half the stains gone.
Lesson from this is, use the right product for the application, water stains on glass are a shit ton harder than you think, and if your going to be doing a lot of glass (I will eventually do my windshield) invest in a 4"-6" orbital polisher.....and a larger bottle of polish.
