Water shut-off valves are small, oval-shaped metal knobs that open and close water flow to household plumbing devices. There is a separate water shut-off valve for each toilet, sink and shower inside a home. The valve is intended to shut off water quickly in case of a malfunction to prevent flooding. Because the valve handles aren't turned very often, it is not unusual for them to become stuck in the open position.
Drop one to two drops of any type of household oil onto the pipe stem next to the bonnet nut. The bonnet nut is located where the valve handle attaches to the pipe. Allow the oil to penetrate for 30 to 60 seconds.
Place the jaws of a wrench around the bonnet nut and tighten them so that the wrench tightly grasps the bonnet nut.
Turn the wrench counterclockwise one to two degrees, just until you feel the bonnet nut start to move.
Grasp the handle of the water shut-off valve and turn it to the closed position.
Reset the wrench on the bonnet nut and turn it clockwise to tighten.
Wipe away any excess oil with a paper towel. Be sure to turn the valve to the open position to restore water flow.
If you still can't turn the frozen water shut-off valve after following this procedure, you should replace it To prevent water shut-off valves from sticking, turn them off and back on at least twice a year.