The two most common kinds of toilet leaks are caused by problems with the flapper or the refill valve.
Replace your Toilet Flapper
A flapper is a piece of rubber that serves as the seal at the opening of the water tank. The rubber can break down over time and cause the seal to be incomplete and water to pass through. You will need to shut off the water supply to the toilet before removing and replacing the flapper. Bring your old flapper with you to the hardware store to ensure you purchase the right one. Sometimes the entire flush valve will need to be replaced, you can do this yourself or hire a plumber to fix it for you.
Adjust your Refill Valve
The fill valve on your toilet determines when the tank is full and the water to the tank should be shut-off. If it is malfunction your tank will be filling continuously. If your valve has a ball that floats at the end of a rod, lift the rod and see if the sound of the tank filling stops. If so, you know that it is the fill valve that is causing the problem. You can then gently bend the float arm so that the ball sits lower in the tank or if your toilet has a way to adjust this fill valve you can adjust it accordingly. You don’t have to empty the tank to do this.
Save water and money
Large quantities can be lost by a leaky toilet. This can lead to increasing water & sewer charges for metered customers. Homes that have private wells may see increased electricity bills due to increased pumping caused by leaks. Most repairs can be completed fairly inexpensively and can be done by the homeowner. If you aren’t comfortable doing this yourself hire a licensed a plumber.