If you've tried to shut off the water supply for your toilet and found that the water doesn't want to stop, it may be time to replace the washer on the toilet's water shut-off valve. These valves, mounted on the wall just behind toilets and other water fixtures, allow you to cut off the water supply without having to disturb the water supply for the rest of the house. As with most plumbing projects, keep plenty of towels on hand when replacing the shut-off valve washer.
Shut off the water main for your house. The main shut-off valve is usually located near the water meter. In a house, this could be buried in the front or side yard inside a utility box. In an apartment or condo, this could be on the outside of your building or inside a utility closet.
Flush the toilet. Hold down the handle as you flush, and allow all the water inside to run out.
Place a towel on the floor under the shut-off valve. Loosen the valve stem by turning the hexagonal nut located just under the handle counterclockwise. Pull the stem out of the shut-off valve.
Remove the screw holding the washer in place, using a screwdriver. Pull the washer off the stem. Insert a new washer in its place. Secure with the screw.
Apply pipe compound to the threads on the valve stem. Use a finger or piece of towel to rub the compound into the threads.
Insert the stem into the shut-off valve. Tighten by turning the hexagonal nut clockwise. Wrap the threads on the outlet with plumber's tape. Reconnect the water supply pipe or hose.
Restore the water supply.
To help keep the washer connection watertight, apply a few drops of silicone grease to the washer face.