At one point or another, nearly all windows leak, which can be a significant issue due to mold concerns in your home. Mold and decomposition organisms require water to grow, and this growth is often out of view inside your walls. To determine where your window leak is coming from: Check your window exteriors two times a year for damaged or peeling caulk Check the gasket or sealant between the window glass and the frame Double-paned windows will have a band of metal on each of the four sides to seal the glass itself. If this fails, moisture may appear between the glass panes