Originally Posted by Deeboe
Vinegar can dissolve/loosen the minerals that are attaching themselves to the glass. You can put some vinegar on a paper towel and try wiping across the water spot. If it does nothing, then try soaking a piece of paper towel and then placing it on the water spot for 4-5 minutes. The minerals are in the water, water dries on the car and/or glass and the sun "bakes" them on the surface. To minimize this from happening, you want to do whatever you can from letting water dry on your car. Rain water is not so bad, but city water often is hard-water and can really do a job on a car's finish. If the vinegar does not work, then use one of the above products for removing them from glass...do not try using them on the paint. Using Rain-X on a monthly basis will prevent water spots from forming on the glass.