Toilets are the leading cause of household water leaks. Yet they are easy to detect, and relatively easy to repair. Even a small toilet leak can cost you $50 or more per year in higher water and sewer bills. Large leaks waste much more.

When your toilet is functioning properly, water moves from the tank to the bowl only when the toilet is flushed. But when a toilet is leaking, water moves from tank to bowl on its own. You may notice that your toilet seems to flush by itself; that is a definite sign of a toilet leak.

Testing for a toilet leak consists of dyeing the water in the toilet tank, either with a few drops of food coloring or a dye tablet provided as part of a leak detection kit, available from your hardware store or water provider. After dyeing the water, wait 20 minutes or so and check the water in the toilet bowl. If it is still clear, then no water has leaked from the tank. If it has even a tinge of color, then your toilet has a leak. Sometimes, if you have a very bad leak, the toilet will flush by itself, and there may be no color visible in either the bowl or the tank.

While there are several possible causes, by far the most common source of leak is the valve that controls the release of water from the tank to the bowl. In most toilets, this is a rubber flapper valve. Depending on water quality and whether you use a toilet bowl cleaner in the tank, these flaps may last from 2 to 7 years.

Replacing a flapper valve is not difficult. For detailed instruction, see www.toiletology.com

Replacement flapper valves are not expensive, running from $3 to $10, but they come in a bewildering array of slightly different shapes and designs. When you go to the hardware or home improvement store to get a replacement flapper, take the old one with you. Some flappers are early-close flappers required by ULF toilets. Replacing an early close flapper with a standard one will result in large amounts of water being wasted. Conversely, replacing a standard flapper with an early-close one may result in the toilet not clearing waste from the bowl.

If you do use an in-tank toilet cleaning product that contains chlorine or other harsh chemicals, consider spending a little extra for a flapper valve made of composite rubbers that are more resistant to these chemicals.