After i have finished washing my car and dried to get rid of water marks i get a cloth that i use for buffing up after waxing and just wipe it down all over windows to and it brings it up spotless!
I mean when you wash the car 1 side of the car drys and starts to elave marks but i heard there was something out there you spray on the car to help the process be longer stopping it doin this so that it gives u longer time to dry the car with a water magnet