I can highly recommend
Autoglym Glass Polish 
Use a small amount on an applicator on the offending water spot, work it until it's dry/powdery and then buff off with a clean microfiber.
If you are still seeing them, you can use the polish gently with very fine steel wool (0000 grade) and then use just the polish as above, to finish off. I haven't tried the steel wool method, but I've heard it does work, just use straight lines when polishing.
