Unlike water leaks that can be resolved with a quick coat of caulking a window leak from the bottom is typically a sign of a much bigger issue.
Roof leaking bottom window.
Window leaks can result from a structural failing elsewhere in the home such as an opening in the roof upper floors or siding.
Start low soaking the area just above where the leak appears in the house.
For example soak the downhill side of a chimney first then each side then the top on both sides.
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.
Remove damaged exterior caulking clean the window frame and recaulk.
You can try some simple maintenance work such as.
Have a roofing expert conduct an inspection of your roof system.
Re seal the glass to the gasket with clear silicone caulk.
If a leak is difficult to find enlist a helper and go up on the roof with a garden hose.
Recaulk the corner flashing if any areas have hardened caulk.
Replace any missing or rotted siding above the step flashing on dormers.
Check the gasket between the window frame and the glass.
Make sure the sill at the bottom of the window frame is pitched.
The problem is often with the window itself instead of anything that you might be able to do to prevent water from coming in.
Unfortunately this may not be the case for water leaking from the bottom.
Sometimes leaking water is finding its way into your through your window sills or frame but is actually coming from your roof.