If your bathroom faucet has only one handle, then you have yourself a washerless or seat and spring faucet. Inside it contains an ball assembly that houses the seats and springs. "What are those?", you ask. Seats are two small rubber cups with holes in the bottom. They sit on top of springs that put them in constant contact with the water-supply valves inside the faucet body. If you see your faucet dripping from the spout, it is probably because the rubber seats are worn.