To fix a leaky bathtub faucet, turn off the main water valve, remove the faucet handle and plate, remove the old O-ring and replace it with a new one and replace the faucet plate and handle. Most leaks are caused by a worn out O-ring. If this does not fix the leak, it may be due to a leaky pipe.
The O-ring on a faucet tends to dry out in time, which causes the faucet to drip. Replacing it is a fairly simple task.
Step 1: Turn off the water and take apart the faucet
Turn off the water at the main water cutoff valve. Remove the faucet handle by loosening the screw. Remove the plate around the faucet by removing those screws.
Step 2: Remove the valve stem and O-ring
Use pliers to grasp the valve stem and remove it from the faucet. Remove the O-ring from the valve stem and replace it with a new one. Use some silicone grease to make it slide on easily.
Step 3: Put the faucet back together
Replace the valve stem, with the new O-ring in place, back into the faucet. Put the faucet plate back in place and secure with the screws, then screw the faucet back into place. Turn the water back on and test the faucet to ensure it no longer leaks.