There are products on the market that are strickly designed to remove hard water spots and acid rain on windows, purchase it and use it and your done. Just do not use it on paint, the products have pumise stone in it and can damage the paint. And do not use the spot remover with steel wool it can score your windows. Read the directions on the label and stick to it. There are other methods of using the product for great results-for your windows, but that requires buffers and other more complex methods. If you stick with the labeled directions you'll be fine. And, you can use the product on chrome, works great actually.
Things that do not work.
Alcohol
Steel Wool
Clay Bar
Buffing Cream
Peanut butter
Window Cleaner especially wind-x
Vinager....
list goes on and on, purchase the hard water stain remover for glass.