Water spots on glass.

use the wax or maguires cleaner wax approach first. If that doesn't do it
try the glass product mentioned by cavemanmoron. I sell for a mercedes,
Porsche,Acura ,Jag dealer and we use those two approaches.
Believe me, the last thing our detail guy wants to do is ruin a $2000.00
heated windshield! We never use steel wool ,even with glass cleaner.