How to Eliminate Water SpotsGet rid of them before they ruin your paint & glass
Water should be a fairly harmless liquid. After all, we drink it, we bath in it and we even use water to wash our vehicles, so how bad could it be? The answer to that question depends on where you live and the minerals that are present in the local water supply. For example, the water in the Southwestern portion of the U.S. is full of hard mineral deposits that will literally etch themselves into paint and window glass if they are left on your vehicle for an extended period of time. Lawn sprinklers are the worst. Leave your vehicle where it gets water-spotted by the sprinklers, then baked by the sun, and the spots are not only difficult to remove, but they may do irreparable damage as well.
Like most problems, the best defense is a good offense. In this case, keeping a good coat of wax on your paint and window glass (that's right, use a glass wax) is the first line of defense against acid rain or water-spot etching. The second line of defense is to act fast to remove any water spots that may get on your vehicle. Time is relative. If you have a dark-colored vehicle and it stays out in the bright sun, you have less time to deal with the problem than a white vehicle in overcast conditions. It all has to do with surface temperature-the hotter it is, the tougher the water spots are to remove.
Removing water spots is fairly easy if you catch them soon enough. Re-washing your vehicle won't do a thing. Instead, mix up a solution of 1/2 distilled water and 1/2 distilled white vinegar in a spray bottle and carry it in your vehicle along with a soft, clean cloth. When you notice water spots, move the vehicle into the shade, let the surface cool down, spray the paint with this water/vinegar solution and wipe it off with the soft, clean cloth. The spots should come right off. Your waxed surface may be dulled by this solution, so apply a coat of wax when you get the chance
If you don't like the smell of vinegar and don't mind spending more money, commercial water-spot removers are available at most boat shops. They work the same way: Just spray the surface down and wipe off with a clean cloth. (I've found the white vinegar just as effective and a lot less expensive.) What if the water spots have gone too far and actually etched the clear coat of your paint or the window glass? More drastic measures are called for. For window glass, try a good dry scrubbing with 000-grade steel wool to remove the spots without damaging the glass. If that doesn't do the job, then the windows will have to be polished with a commercially available glass polish and a power buffer.
Because today's water-based paints are very delicate (especially the clearcoat), you'll want to experiment with the least-aggressive polish available. Try hand-polishing with a cleaner-type liquid wax. If the spots persist, then have a professional buff the surface with a fine polishing compound and machine buffer. Follow with a good hand waxing. Today's clearcoats are very soft and thin, so make sure that everyone who attacks water spots with a power buffer knows what they're doing. Ideally, you'll keep the water/vinegar "first aid kit" handy so that the water damage will never get to this point.
New vehicles and new paint jobs are expensive. Keeping your vehicle looking new will add miles of driving pleasure and protect your investment.