I don't mention it unless asked, if asked I tell them it's pure water and because
there's no soap in the water the rain won't make any difference to the glass as it's the soap that causes the worst water marks
I finish by telling them I will re clean any windows they are not happy with no mater what the weather.
What I find amusing sometimes is if a custy complains about you working in the rain
after cleaning them and they have dried ask them to show you the windows in my experience they can't, Top three replies are
I had to go and clean them myself
I haven't had a chance to look at them yet
(Ask them to look now)
It's dark how can I see if there clean in the dark