Leaking toilets waste more water than any other fixture in the home. Even a silent toilet leak (that’s one you normally can’t hear) will waste from 30 to 500 gallons of water per day! The ones you can hear will waste much, much more. Such wastage can normally be attributed to a faulty water level adjustment or to a leaky flapper.
Most people will say their toilet does not leak. However, there is a way to find out for sure. Put some dark colored food dye in the tank then watch to see if the colored dye is entering the toiler bowl. If there is color, or if you already can hear and or see water running in your bowl, it’s time for a new flapper!
After installing the new flapper, run the dye test again to assure you have no leak. If the leak persists (and every now and then it will), you are probably going to have to replace the entire flush valve.