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Utilities > Conservation > Save Water  > Identifying and Repairing Toilet Leaks  

The Most Common Household Leak

Dripping faucet.Toilet leaks are the most common household leak, so toilets are the first fixtures to check when your water consumption increases above what you think is normal.  If your meter indicates a leak by constantly turning, your toilet can be isolated by turning off the valve at the wall beneath the toilet tank.  If a valve is turned off and your meter stops turning, you have found the source of the leak.
This information does not apply to pressure assisted toilets. These
toilets can be best identified by the presence of a large, sealed, dark plastic tank that occupies the toilet tank. You should consult the owner's manual for information that applies to this type of toilet. The following are four areas where toilet leaks occur, in the order of most to least common.

Found in all standard toilets, this is the round rubber disk at the bottom of the tank.  By lifting off the lid, you notice that the flush handle connects to the “chain” which connects to the flapper.  By pushing the handle down, the chain lifts the flapper which releases water to flush the bowl.  Flappers last about 3 years before they begin to degrade and allow water to leak from the tank.  This is the most common source of toilet leaks, and is usually the cause of a toilet turning on and off periodically.
Internal workings of a toilet.

 Flapper leaks are not always detectable by checking the meter to see if it is turning.  If you do see your meter turning on and off when no one is using water, or if the toilet seems to flush by itself, the flapper is probably the culprit.

To verify the nature of the problem, first mix some food coloring with the toilet tank water.  If you flapper is leaking, or if your water level is too high, you will see the bowl water begin to discolor within about five minutes, as the food coloring leaks into the bowl.  If your water level does not need to be adjusted (see “Overflow Tube”), you have a leaky flapper.

To replace a leaky flapper, turn off the valve at the wall, flush the toilet, then unhook the old flapper.  There is a round outlet at the base of the tank that the flapper seats against.  Run your finger around the top edge of this outlet to feel for nicks, scratches or other irregularities.  A rough surface here can cause water to leak past a perfectly good flapper.  If the surface is damaged, then you will have to unbolt the tank and replace the seat and the flapper.  You should be able to purchase these parts from your local hardware store. 

Take your old parts in with you, and if all you need is a flapper, try to purchase one of identical design to make sure it will seal against your old parts.  Once replaced, your new flapper can be checked for a good seal by the food coloring method.  If the problem toilet is old and is larger capacity, you may want to consider replacing the toilet with a new high efficiency model.

Overflow Tube.

This is a ¾” diameter tube that rises vertically from the center of the tank.  It empties into the bowl, and it’s purpose is to prevent water from overflowing your toilet, should something go wrong.  High water levels in the tank can cause water to flow down the tube and into the bowl.  Water levels should be adjusted to the appropriate level line, found either on the overflow tube or on the inside back of the tank.  To learn how to make adjustments, see section titled ‘Ballcock’.


Also known as the fill valve, this valve regulates the water level in the toilet’s tank.  If not adjusted properly, it can waste several HUNDRED gallons per day!  If this valve is set so that the water level is too high, water will seep (continually) into the overflow tube.  Ballcocks also tend to wear over time, so that they run or seep regardless of how they are adjusted.  A problem ballcock should be adjusted, rebuilt with new seals, or replaced.

To adjust the ballcock, do not bend the float arm or any other parts to lower the water level, because it may cause mechanical problems.  Water levels may be adjusted by turning the adjustment screw on top of the ballcock.

Fluidmaster® ballcocks are different.  Water levels may be raised or lowered by adjusting the float that rides up and down beneath the ballcock; simply pinch the stainless steel clip at the side of the float, and move it up or down the thin rod it rides on.

Fill Tube

Designed to rinse the sides of the bowl while the tank is filling, this ¼” diameter flexible plastic tube is not found in all toilets.  Beginning at the ballcock, it arches across the tank, and inserts into the overflow tube.

A ballcock may develop a leak through the fill tube that is not easily seen or heard. A common leak is caused by the tip of the fill tube being placed below the water level of the tank – a siphoning action may occur.  To stop the leak, simply lift the end of the tube above the water level, or lower the water to the appropriate level.   

Here’s a Tip from

Phantom Flusher

Do you have a Phantom Flusher? That's a toilet that turns the water on all by itself and lets it run for about 15 to 20 seconds. If you have a Phantom Flusher, you know I'm not kidding.A Phantom Flusher is a built-in feature of some refill valves (also called ballcocks); the device sits in the left side of the toilet tank.

The neat feature of a Phantom Flusher is that it not only tells you when the toilet is leaking, but it also tells you which part in the tank needs fixing --- it's the flush valve flapper, ball or disk that needs replacing.

The flush valve is the unit in the center of the toilet tank with a chain attached to the trip lever. Now, have you got that straight? A Phantom Flush does not mean anything is wrong with the refill valve, the problem is that the tank ball, flapper or disk on the flush valve is leaking and needs replacing.

Now if you're not lucky enough to have a Phantom Flusher in your toilet tank, I have a little trick that will reveal which part is causing a leak. First, remove the tank lid and turn the water off at the supply valve under the tank.

Next, with a pencil, mark the water level on the back wall inside the tank. Wait 20 minutes or so, and then check the water level. If you find the water level remains at the pencil mark, you need to fix or replace the refill valve.

On the other hand, if you find the water level has dropped and is now below the pencil line, it's the flush valve flapper, ball or disk that's the culprit.

Additional Information

More information is available on solving your
Phone. water use problems.  If you need to speak with someone, call the Utilities Conservation Office at 781-7217 or 781-7213.

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