Windows and rain.

Many people are concerned about rain when getting their windows cleaned. It makes sense, you just paid to have your windows cleaned and now its calling for rain. However rain is usually not a problem, the problem is dirt and other debris, which are already on your window. In fact it is actually better to have your windows cleaned before it rains for the longevity of the glass. When it rains, the water from the rain does not wash off the dirt from the glass unless you had a heavy down poor as if you were in the tropics, and even then it might not actually wash all the dirt off the glass. When the water mixes with the dirt and rest on the glass, it makes it easier for the minerals in the dirt to deposit onto the surface of the glass.

By having your windows cleaned before it rains you are helping your windows from having mineral deposits onto the surface of the glass. If there is not a lot of dirt blowing around when it begins to rain, then once the rain dries on the surface of your glass, you should still have very clean windows. As most rain falling from the sky has very little TDS in the water.