Rain alone will not ruin clean windows. There, I've said it.
I want to take on this myth, as many people seem to confuse their houses with their cars. Unlike vehicles, whose nice carwash will definitely be ruined by driving around on wet and dirty roads, your house stays put. When your windows are dirty and it rains, they definitely will look worse afterwards. However, when CLEAN windows are rained on, the rain water does not carry any dirt, minerals, or calcium with it as groundwater does. It will simply dry and any marks left on there will be barely noticeable.
How can I be so confident? I don't offer "Rain Checks", however there have been times when it has started raining during a cleaning and I have offered to come back and touch up any bad marks that the rain has left. In 19 years of business, I've only ever had to return 3 times, and all 3 times were due to issues that were compounded by the rain, not due to the rain itself. You see there ARE some situations in which this won't hold true: rains with high winds blowing dirt onto lower windows (such as during the Monsoons), a dirty roof or leaky awning dripping dirt onto glass from above, oxidation on old window frames or siding washing off on the glass, etc. So, in some cases the wise decision is definitely to reschedule. However, for most jobs, especially where the majority of windows are under an overhang or porch, there is no need to panic.
If you do have concerns and I feel like there aren't any of the above issues with your house, we promise to return and touch up any windows that were affected by the rain. Keep your scheduled appointment and you can be confident they'll look great once our beautiful weather returns!