So did you try to wash it yet? Makes sense that water and a rag wouldn't take off hard water spots, but I've never seen spots that good quality car wash (Meguiar's Gold Class or NXT Generation) wouldn't remove.

I agree with vinegar as option #1, but you might also considering trying Meguiar's Liquid Cleaner Wax. Not expensive (maybe $7?), super-easy to apply, and eliminates water spots with no problem. Just wash the VX first and then apply it.