I've been told a solution of vinegar and water will remove all but the toughest water spots... I evidently have only ever had the toughest ones though, because its never worked for me... newer cars get what we refer to as "acid rain spots" around here, particularly on soft parts, like plastic rear spoilers and urethane bumper covers. Its attributed to the paint being "softer" on these parts to allow them flexibility without cracking... it also allows acid rain to attack the paint easier too though... what I'm referring to are spots with a white "ring" around them, basically "burnt" into the paint/clearcoat.... sometimes they are bad enough that even buffing won't remove them...maybe yours aren't that bad, so with that said, try the vinegar, and keep your fingers crossed... (although that never seems to work for me either!)
