I blame the rock-hard water down here for making window washing more of a chore than it should be.
Minerals not iron. Scrub down a window and let it air dry and the film is so bad, it's awful to see through when sunshine is playing on the glass. Drinking glasses have to be rubbed dry. Seven PSI is not enough for a softener to work. And water is too pricey to flush a softener.
So, wash a window then rush to dry it. Soap is useless. Adding Grain vinegar to the seems to help. I have a TDS meter, and select the planta de agua purificaca with the fewest dissolved minerals for my BiPAP.