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How to Check for a Leak in a Toilet

Leaking toilets are a major cause of high water bills for residential users.  Unlike dripping faucets, toilets can silently leak thousands of gallons in a single month, significantly increasing your utility bill.  A 'running' toilet can waste two gallons of water per minute, a 'silent' leak can waste up to 70,000 gallons per month.  There are several different ways that a toilet can leak, and many different symptoms to let you know there is a problem.  Here is a list of the most common symptoms:

  • If you have to jiggle the handle to make a toilet stop running.
  • Any sounds coming from a toilet that is not being used are sure signs of a  leak.
  • If you have to hold the handle down to allow the tank to empty.
  • If you see water running over the top of the overflow, you definitely have a leaking refill valve.
  • If you see water trickling down the sides of the toilet bowl long after it has been flushed.
  • If water drips out of the refill tube into the overflow pipe. 
  • If a toilet turns the water on for 15 seconds or so without you touching the handle, otherwise known as the phantom flusher.

Some leaks are slow enough that they cannot be observed in a matter of seconds; however there are simple and easy-to-do tests that will let you know if you have a problem.

Dye Test

Remove the tank lid and add some instant coffee, powdered fruit drink, food coloring, or other water soluble non-toxic dye to the water.  Add enough to dye the water a deep color.  (If you are currently using an in-tank colored bowl cleaner, remove it first and flush several times.  You can the re-insert it and use the bowl cleaner to dye the water instead).

Make sure nobody uses the toilet for the next half hour.  After 30 minutes, look in the toilet bowl.  If the water in the bowl has been colored by the dye in the tank, the toilet is leaking.  This may take several times trying; toilets may intermittently leak down between flushes.

Toilet leaks are typically (but not always) caused by a worn out flapper valve or a fill valve that doesn't completely shut off when the tank is full.  The flapper valve is the stopper in the bottom of the tanks that lifts up when you push the flush handle and is the most likely culprit.  The solution:  Replace your flapper.  Shut off the water at the toilet, not at the house line.  Remove the worn flapper and replace with a comparable flapper valve (you can ask your hardware retailer for assistance in choosing the proper replacement.)

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