I wasn't going to comment, but I will...
At least 80% of my residential clients do not want their windows cleaned in the rain. No matter what I tell them that is it!
I give them all the pros about purified water etc etc, they say, "well I still don't agree. Mine have never been spotless after heavy rain".
You'll now say i'm not cleaning them right. Blah blah blah.
I don't do residential in heavy rain.
20 years a windowcleaner 2 years wfp in an economically depressed area.
That's just the way it is.
If it's different for you, well done, but it may not be just down to what a brilliant cleaner and businessman you are.