If you notice water stains on the wall above the window or along the top or bottom of the frame this usually means there is a leak inside the walls.
Roof leaking bottom window.
If a leak is difficult to find enlist a helper and go up on the roof with a garden hose.
Window leaks can result from a structural failing elsewhere in the home such as an opening in the roof upper floors or siding.
Dig out any cracked or dry caulking that isn t properly sealing adjoining surfaces and replace with silicone caulk.
The problem is often with the window itself instead of anything that you might be able to do to prevent water from coming in.
Check the gasket between the window frame and the glass.
Replace any missing or rotted siding above the step flashing on dormers.
Unfortunately this may not be the case for water leaking from the bottom.
You can try some simple maintenance work such as.
Remove damaged exterior caulking clean the window frame and recaulk.
Isolate areas when you run the hose.
Recaulk the corner flashing if any areas have hardened caulk.
Have a roofing expert conduct an inspection of your roof system.
For example soak the downhill side of a chimney first then each side then the top on both sides.
Sometimes leaking water is finding its way into your through your window sills or frame but is actually coming from your roof.
Missing shingles or a failing roof system might be your culprit.
Make sure the sill at the bottom of the window frame is pitched.