Out here in the mountain west the groundwater is heavily mineralized and only a day or two of sprinkler overspray will leave the ugliest water spots you've ever seen, bad enough to catch your fingernail on sometimes. I've tried just about every normal method out there including several cleaner waxes, the clay bar, etc. None of them have really been very effective and only cover up the spots a bit or have a minimal effect.

One day I decided to try Scrub Free soap scum removed which is a mild acid. Most of the cleaners of this type say not to use on painted surfaces, but Scrub Free doesn't and its also a different type of acid from most others, so I gave it a shot. I wet the hood pretty well, sprayed a bit on and rubbed lightly with a damp terry cloth towel. I left it only only about a minute before rinsing VERY well. In about 5 minutes I got better results than a couple of hours with any other method. Sometime I've had to repeat the process 2 or 3 times, but the spots evetually disappear.

I might be doing some mild long term damage but I haven't seen any. I always follow-up with a good cleaner wax afterward. The only downside I've seen is some slight discoloration of plastic parts if you don't get it rinsed off quickly. I little Back To Black seems to clear that up mostly.

It works for me, and I haven't found anything else that does. Use at your own risk though

Kurt