There are several types of faucets, some are single lever, and others have both hot and cold knobs.
If you have a faucet leak it is necessary to know if you have a washer and seat type or a cartridge type. A washer and seat type of faucet is designed to have the washer attached to the part of the faucet that moves when you turn the handle either open or closed. As you turn the handle the washer either gets farther away from the seat, when you open the faucet, or closer to the seat as you close the faucet.
If you have a faucet that drips after you have shut it off, even after you try to tighten it, you may have a bad washer. Before you do anything you need to go to a hardware store and get an assortment of washers and brass screws so you don't have to take the faucet apart twice. Since the washers are cheap it will be a time saver to just get a few extras.
Once you have the washers turn off the water supply to the faucet and remove the faucet handle. Then remove the large nut right below the faucet handle and unscrew the stem (the part that the handle attaches to). With the stem removed you will find the washer attached to the bottom of the stem. Unscrew the brass screw that is holding the washer and remove the old washer. Match-up the old washer and screw with a new one and install the new washer and screw.
With the new washer and screw installed you now need to check the seat that the washer makes contact with in the faucet. Look down into the faucet with a flashlight and check to see if the seat is intact all the way around it. Depending on how long it was dripping it may have worn a groove in the metal. If the seat looks smooth then just replace the stem with the new washer and the leak should be fixed. If you noticed that the seat has a groove worn into it you will need to touch-up the seat with a tool designed to do that. The seat tool can be found at a hardware store. How the seat tool works is you hold it up against the worn seat and grind the high edges of the seat down to meet the height of the worn part of the seat. After you are finished grinding the seat it should be flush all the way around so when the washer comes in contact with it the water flow will be completely stopped.
The seat grinding tool is not very expensive and it is easy to use. You just turn it by hand, it is not a power tool.
