In a rainstorm you may see water at the top of the foundation running down or leaving a stain.
Superhydrophobic wall siding leaking water.
Water leaks at soffit or eave overhang penetrations for chimneys that permits water to leak at the roof surface then pass behind the siding if the chimney is not properly flashed.
Wood siding leaks damage.
Cut a hole in the wall large enough for your head to fit inside.
Vinyl siding installs in pieces so gaps and overlaps.
Then using a drywall saw cut along the line you just scored.
My photo above of ice below some courses of vinyl siding traces a moisture problem traced to improper installation of a through wall vent for a direct vent heating appliance.
The wood clapboard sided home shown above located in poughkeepsie new york was badly damaged by leaks into the wall that ensued from yankee gutter leaks and downspout leaks below a roof valley.
Although vinyl is impervious to water when installed as directed by the manufacturer vinyl siding as a whole is not completely watertight.