those must be some pretty stubborn water spots...sometimes the polarizied effect of tinted windows (factory tint I mean) can look like spots when its really just the glass and that leaves nothing to do...if you really do have stained glass then try some of the cleaning compound as used for aircraft, that actually cleans and slicks the glass so moisture will run off and not bead...or you can ask someone at a local high end parts store that carries the Meguiar's line of showcar care products...Meguiar's makes an extensive series of products and I'm sure they make a glass cleaner similar to the aircraft type...there is also a polish out there called "liquid glass" but it is a polish and therefore has very little abrasive in it. Liquid Glass will slick the glass to keep water from beading but it will not remove any existing stains...a good home remedy for cleaning (if you can take the odor)is one part alcohol, one part vinegar, to six or seven parts water, then wipe the glass with newspaper...I know it sounds crazy but it will get off just about any case of road grime out there...hope this helps