When I've had that happen before I would up just giving it a quick wax job. I started using the old Mr Clean system and it eliminates all water spotting. One product I have bought that really does live up to its advertising. Getting hard to find refills tho.
If the water spots are in the clearcoat, I would suggest getting a clay bar from Mother's. and then waxing after you finish the process. If that doesn't work, I would suggest buffing the car with 3M's finesse-it and a polishing pad, then waxing after you've buffed it.