In-line water valves, or shut-off valves, are installed into the household water line. They control the flow of water into the pipes that serve all water fixtures in the home. The valves are either soldered or threaded into the water line, and either have a circular dial or lever that turns the water on or off. Shut-off valves tend to leak if the packing nut is loose, or if the packing washer is old and needs replacing. Either way, fixing the valve is a simple process and doesn't take much time to complete.
Place an adjustable wrench around the packing nut directly under the valve's lever or dial and make a 1/8 clockwise turn. Make another 1/8 turn if the valve continues to leak. If it still leaks after the second turn, the packing washer needs to be replaced.
Turn off the water supply at the city shut-off valve. Remove the dial or lever's screw with a screwdriver. Take off the dial or lever.
Place the wrench around the packing nut and turn it counter-clockwise to loosen the nut. Remove the nut. Pull off the packing washer positioned under the nut and put on a new washer. Thread the packing nut back into place and tighten it with the wrench.
Replace the dial or lever. Turn on the water and open the valve. If the valve is still leaking, tighten the packing washer with the wrench in 1/8 turns until the leak stops.