How to remove hard water spots from car glass?

Glass polish and a random orbital will remove the spots. If you don't have a R/O you can remove the spots by hand as well. A polish that works extremely well and removes easily is the Zaino product.

 

I have used many glass polishes over the years. I would recommend using Auto Finesse Vision as it is a superior glass polish. It can also be used very easily by hand. To get faster results, you can also use most any glass polish with a rayon glass polishing pad. I believe Griot's sells 3" and 6" glass pads which can be used on a D/A or by hand. If water spots are extreme and more cut is needed, then I recommend using CarPro Ceriglass. Ceriglass has cerium oxide in it which can actually polish scratches out of glass when used by machine.

 

Bar Keepers Friend (Cleanser) Found in most Super Markets and Hardware stores
I have been using this for glass since long before ther were all these specialty products
12 ozs. is less than $2.00.
As always try it on something, or in an area that does not matter to get an understanding of its use prior to trying it on the final surface.
I've used this for windshield water spots on everything from VW's to my F-cars
I-net is your friend for info

 

Glass stove top cleaner.

 

To reduce build up, do your regular window cleaning with one of the window cleaners that contain acetone. Depending how bad it is, that may be all that is needed to remove the spots.