Leaks inside your toilet can waste up to 200 gallons of water per day and can be difficult to detect with the naked eye. To find a leak, add a few drops of food coloring to your toilet tank and wait a few minutes, don’t flush.
If color appears in the bowl then you have a leak and repairs should be made.
Normally, leaks are caused by a bad flapper valve, flapper valve seat, ballcock valve, improperly positioned float arm or a defective overflow tube.