The problem with water spots is the huge variety in their make up - MDR (IMO) is good at removing light water spots, the kind you get when rain falls on a dusty car. Hard water from a faucet may take more effort. The toughest water spots I've dealt with come from well water and wheel acid (with some agitation) removed them. Wheel acid will not damage Opti-Coat Pro and I believe if removed before drying, is safe on clear coat. I can't speak to glass, but if like Power Clean, the key is rising well before the product dries.