Do you have a phantom flusher? Does your toilet sound like it's running all day? You may have a leak. More than 20 percent of gravity-flush toilets leak.
Follow these tips to find and stop toilet leaks. If you are not sure about your ability to perform any of these steps, please contact a licensed plumber.
Note: These tips pertain to traditional gravity-flush toilets and not high-efficiency toilet models.
A continuous trickling sound usually means water is running over the top of the overflow tube inside the tank. The periodic sound of water being added to the tank usually means a leaky flapper at the bottom of the tank.

"Ghost" or "phantom" flushing is usually the result of a worn rubber flapper that is allowing water to seep from the tank into the bowl and down the sewer. An improperly adjusted flapper chain also could cause the problem.
Conduct a simple dye test to see if water is seeping from the tank. Request an Indoor Water Audit and Retrofit Kit, which includes leak detection dye tablets. Or, use food coloring or a powdered drink mix to noticeably color the water in the toilet tank.
Note: If you normally use products that color the water in the tank or bowl such as a sanitizer, remove them and flush the toilet until the water in the bowl and tank are clear before you begin the dye test.
Turn off the water supply valve to the tank. This is usually located on the wall under the toilet. Flush the toilet to drain the water.
Select appropriate replacement parts from the hardware store and follow the manufacturer's directions to install them.
After installing the parts, turn the water on and test-flush the toilet once or twice. If you replaced the flapper, perform the dye test again to ensure the flapper fits properly. Not all flappers fit properly in all toilets so you may still have a leak.
In some cases, a leaking flapper may be the result of a worn surface on the seat against which the flappers rests. You can try smoothing the seat with steel wool or a scouring pad. If this doesn't correct the problem, you may need to replace the flapper seat and overflow tube assembly.
Most major plumbing manufacturers have detailed assistance on their Web sites as well as toll-free telephone numbers to call for assistance.