Article: In some places the minerals in the groundwater, lime, magnesium, and calcium in particular, will cause spots to appear. If you notice crusty buildup on your car windows that is stubborn and won't come off, you probably have hard water. You'll need to clean the hard water spots as soon as possible. Hard water spots that can etch the glass of your car if left for too long on its exterior. Thankfully, your hard water problem can be taken care of with just a few household supplies. Vinegar, specifically, is an exceptionally good cleaner when it comes to removing hard water stains. For your hard water cleaner, you'll need: Cloth (microfiber recommended; clean cotton OK) Distilled water Spray bottle or bucket Rubbing alcohol White vinegar If your windows are still looking cloudy or less brilliant than you'd prefer, you may need to apply some polish to your car windows. You'll want a polish that doesn't contain oils, as these are included to help polish paint, but you should be able to find a multi surface finish restorer that'll work on car windows at your local hardware or auto store. When polishing, use a soft cotton cloth or an old, clean, soft fabric t-shirt.

What is a summary?
Identify hard water buildup. Assemble your supplies. Polish your glass to restore hard water damage.