I have some pretty tenacious hard water spots on my windows and mirrors. Anyone have tricks for removing them?
DD, Here is a article that was found on Toyota Nation for your problem. Claying seems to remove alot of problems with paint.
Water Spots
The same water you use to clean your vehicle can also damage your vehicle paint. The spots and damage are caused by the minerals in the water. When water evaporates off of your vehicle paint, it leaves behind the trace elements it contains. Calcium and metals are the most damaging elements found in your tap water, whereas rainwater may contain damaging acids from air pollutants.
Avoiding water spots is easy if you chase after them. The best solution is to use a quick detailing spray after you wash, or as soon as you discover the spots.
You can first try Claying, but sometimes even clay won't do the job.
If the spots are allowed to dry and bake on, they will attach to and harden on your paint. When this happens, you need to use a mild acid to get them loose. Believe it or not, the best acid is also the least expensive and most available: a gallon jug of distilled white vinegar.
Expert car detailers have known this secret for years. If you take your car to a pro, they will tell you about the "magic acid bath" and charge you $60 or more for the pleasure of smelling like a pickle. Save the $60, put on some gloves, and do it yourself. Just get the cheap vinegar. No need to get the scented kind.
To give your vehicle the magic acid bath, first wash your Taco with your normal car shampoo, rinse, then use the distilled vinegar. Just wipe it on with a sponge, and rub it in. Do one section at a time, let it sit 30 to 60 seconds, then rinse. When you're done, wash the car again with shampoo and rinse. By the way, vinegar will remove your wax. So, be prepared to re-wax your car after the vinegar treatment.
If water spots are allowed to stay for more than a week or so, the minerals can etch the paint. In this case, using vinegar will remove the mineral spots, but the paint will have etched spots (dimples). In this case, it is necessary to use a medium cut polish (if you have a polisher) or a fine cut polishing compound (for use by hand) to restore the paint surface.