If you have a leaky faucet you may find all that is needed is a new valve stem and washer. The valve stem is located under the handle of the faucet. They can rust over time, or the threads could have stripped when a prior owner installed or worked on the faucet. Fortunately this is a fairly quick and easy fix for an annoying problem.
Step 1 - Turn Off the Water and Faucet
Turn off the water supply to the house. The main water valve should be located by the water meter, usually outside the house. Turn the valve clockwise until it stops. Then, turn the faucet on to release any excess water in the pipes.
Step 2 - Cover the Drain and Open Handle
Once the water pipes are empty, cover the drain in the sink with a rag or other item to keep small parts from accidentally falling into it. Then, look at the handle on the faucet, and check for a cap in the center. This will be covering a screw that secures the handle in place, so when you see it, pry it off with a flathead screwdriver; if you're unsuccessful, try a channel lock pliers instead.
Step 3 - Take Notes and Remove Screw
It is a good idea to list on paper the order in which you remove parts so it's easier to reassemble the faucet later. Depending on the type you have, you may find there are more parts to be removed than expected.
Under the cap you will see a screw. Take the appropriate style screw driver and turn the screw counterclockwise to remove it.
Step 4 - Remove Handle and Disassemble
Slide the decorative handle off of the stem and set it aside. Remove the collar from around the stem as well. Depending on the type of faucet you are working on and how old it is, there may be several other parts to remove before the collar and stem can come off. In a newer simple system, there is usually only the collar, but older faucets, especially bathtub faucets, may have a knurled fitting that can be removed with a channel lock. There may also be some hexagonal parts that you will have to use a wrench to take care of.
Step 5 - Remove Stem and Go to the Store
Using a valve stem wrench or channel locks, remove the stem. Bring this part to your local hardware or plumbing supply store to buy a replacement. You will not know what kind of stem you need prior to taking the faucet apart, so do not buy it in advance. Odds are you'll just have to take it back. Instead, wait until you have the old one in hand so you know for certain you're getting the right piece.
Find the same stem at the hardware store. If you're having trouble, ask for assistance to make sure you are purchasing the right part. A new washer is usually included with the stem but double check just to be sure. This is located in the recessed end of the stem.
Step 6 - Check the Washer and Replace Fittings
Before installing the new stem make sure the washer is installed in the bottom of the stem securely. It should be snug in the recess.
Put the new stem into place and, if applicable, replace the fittings and hexagonal parts. Refer to your notes to reinstall in proper order and tighten everything securely.
Step 7 - Replace Parts and Test
Replace the collar, decorative handle, and screw, making sure the screw is tight. Turn the main shut off back on, and test the faucet. If there is no leak, you have solved the problem, and you can finally pop the handle cap back in.