Water spots can be a total pain in the **** because they can actually etch down into the paint. In some cases a vinegar/water wash will do a great job, and sometimes a clay bar will be sufficient. But the clay bar only works on above surface contaminants, like the mineral deposits left behind. But if they are actually etched into the paint, a clay bar won't do a darn thing and you'll need a paint cleaner instead. The fact that the TW Ice Liquid Clay Bar helped doesn't suprise me - this product is terrible as a clay bar substitute and is nothing more than a mild paint cleaner, but that means it can have its uses. Had the spots deeply etched, however, I'm sure it would have been ineffectual. Hell, I've seen water spots so badly etched that even a rotary buffer with a wool pad and a moderate compound didn't get them completely out. Wet sanding was the only recourse. Yes, that's an extremely rare case, but it goes to show just how far this problem can go.