Get the car into a shade. Try soaking some paper towels in household vinegar and spread them on the windshield and let them sit there for 10 mins. Then scrub the windshield with them before throwing them away.
Barkeepers' Friend .Found at most anyplace houshold cleaners are sold.Its an non-abrasive powder that you can mixdown or just sprinkle it on the windows dry,then use a wet washcloth to lightly scrub,rinse,dry it'll look factory clean.
I did some research on water spots a few months ago for my boss. Water spots are actually pits in the glass. So unless you find a way to polish them out they are permanent.