Originally Posted by Mike-in-Orange

Water spots can be a tricky thing. A wash with a cup of distilled white vinegar in a gallon of water might do the trick, it might not. A clay bar might do the trick, it might not.

Vinegar will help to neutralize and remove mineral deposits, to a point. Clay will remove any bonded surface contaminants that those mineral dposits might have left behind. But there is a third scenario, and it's not good. Fortunately, it's also not real common. There is a possiblity that whatever was in the water and subsequently left behind could actually etch the paint. I had to deal with this on a Corvette last year and the only thing we did not do was to wet sand the affected areas and then buff out the sanding marks. I know that would have done the job, but the owner was terrified of the process so we held off. We managed to minimize the appearance with some heavy polishing using a wool pad on a rotary polisher with some fairly aggressive compound. It was a total pain.

Again, this is very rare, but it does happen. I would do the vinegar/water wash, then clay, then go at the whole vehicle with a good paint cleaner, then wax it. If yoiu can find a good detailer in your area you might want to pay to have thing taken care of by a pro. Keep in mind, that the guy who charges $100 at the local full service car wash is probably NOT the guy you want touching your car. He's likely to attack it with an old wool pad on a rotary, instill a bunch of holograms and swirls, then just cover them up with a heavy glaze and call it a day. The car will look great for a month, but after a couple of washes the glaze will be gone and the mess will reappear. A pro, a real good pro, will likely charge something in the $350 to $500 range, but he'll do the job right the first time and actually correct the problems for you.