Chemical Guys sells a water spot remover that is a gel like constancy. You rub it on and let it sit it will eat away the calcium etc. then just rinse it off. very good product. You need to be careful will water spots because if they are not taken off properly the result would be to take off a lot of clear coat to fix the mistake. It works on glass too.
www.chemicalguys.com they dont have it on their site. Call and ask for Paul tell him Jonathan sent you. I think it is about $18 or so
if you dont want to call you can get it here
http://www.detailedimage.com/Chemica...-Remover-P194/