If you've ever noticed that your window sills are cracked? It may be due to the age of the home, but is likely caused by a much bigger problem. This is a telltale sign that water is getting into the home and causing damage. This can be caused by a few things: Leaving a window open when it rains, not wiping/drying the sill when it DOES collect water, improperly installed window. If our competitors installed your leaky window, then we would certainly start by inspecting their installation process. An improperly installed window can certainly lead to a window leak that may require more attention later. The pictures above were cracks believed to be caused by a window air conditioning unit that was not properly installed or efficient.