Pristine Pole cleans windows irrespective of the weather,the Pure water that I use to clean windows which has the same chemical breakdown as pure rainwater.
I recently tested the rain (Aug 14 Poole,Dorset) with my meter which measures Total Dissolved Solids (TDS) in water, TDS is the description for the particulates that leave water marks and spots on your glass. I collected the rain water in a clean beaker and tested the content. I established that the TDS reading of the rain water was 0 Parts Per Million (PPM) Ie 100% Pure. Interestingly, I then passed the same water through some relatively clean guttering and found that the water have already picked up enough particulates to change its reading to 60PPM.
So, essentially if it rains during or directly after I’ve been to clean your windows there is no need to worry, the rain directly hitting the glass is ordinarily clean and will not affect the finish.