For two-handle faucets, known as compression faucets, leaks are typically caused by a worn washer. These faucets are easily repaired by removing the handle and replacing the worn part. However, most tubs and showers today operate with a single-handle faucet, which opens and closes with a cartridge rather than a compression system. If the spout is leaking, either an O-ring on the cartridge found inside the handle, or the entire cartridge, is damaged.
Turn off the main water valve that provides water to the bathtub and open the faucet handle to relieve the pressure.
Remove the handle cover cap by prying it off with the blade of a pocket knife.
Unscrew and remove the central handle screw, using a Phillips screwdriver.
Pull off the handle.
Remove the clip that is holding in the cartridge, using needle-nose pliers.
Pull out the cartridge. If you cannot remove it by hand, cartridge puller wrenches are available.
Examine the cartridge. O-rings are located at both ends. If one or both appear corroded or damaged, cut it or them off with a utility knife. If the entire cartridge appears corroded or damaged, take it to the hardware store to buy a replacement.
Coat replacement O-rings in heat-resistant silicone grease and slip them onto the old cartridge. If you are replacing the cartridge, coat the O-rings already on the cartridge with grease.
Reinsert the cartridge with new O-rings or the new, replacement cartridge and secure it in place with the cartridge clip.
Press on the handle, screw in the handle screw and pop the handle cap back on.