Okay, I spend a lot of time detailing. If you have issues with water spots there are several options:
1. Stoner's invisible glass : great product, available at most auto parts stores
$4 a can, window tint safe
2. If you have hard water, they sell a treatment you can add to your wash bucket that will stop water spots from forming.
Here are 2 great web sites for detailing info and products:
www.properautocare.com - family owned out of Tampa, I've bought from them for over 15 years
www.autogeek.net - great customer service
both websites have tons of detailed instructions for fixing minor issues to preparing for a car show