Use a utility knife to score a line about 10 inches 25 cm long into your drywall at the location where you see visible signs of a water leak mold discolored drywall etc.
Superhydrophobic wall siding leaking water.
Wood siding leaks damage.
In a rainstorm you may see water at the top of the foundation running down or leaving a stain.
Ultimately water began to appear on the floor of the kitchen inside.
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.
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.
Cut a hole in the wall large enough for your head to fit inside.
If it is a cantilevered area as in this case place your hand at the base of the wall and feel for.