I have an old wave runner (sorry guys) with a ton of water spots on it. I have tried almost everything recommended in this forum. Bon-Ami seems to be very recommended here for water spots and I will tell you that Bon-Ami did nothing. Vinegar - nothing.
While we are at it - what do you guys do to keep water spots off your boats? My new boats has a charcoal colored hull and deck which is going to show every water spot.