I agree with Jeff that are more and likely to have come from the building,
the main cause for this is the adhesive used to attach the small stones to
the building. The water then runs under the top sill and then onto the window,
this is either bad building design or wear and tear on the building. The water
should run down without running down on to the next window below.
WFP would not be the main cause for this, it happens when the rain hits
the building and then runs down the building. On many a new estates that
I clean some windows have been contaminated with these spots, you
cannot get them off. It is down to poor building design and poor builders.
Doug
