Testing for Water Leaks

Reasons to Test for Water Leaks
Water leaks are costly. Slow drips of water can add up quickly. A toilet that keeps running after you flush or a sink that drips after it is turned off can waste thousands of gallons of water a year and add thousands of dollars to you water bill. If the drip is hot water, you are paying for wasted energy too. Fix leaks as soon as you find them. They won’t go away on their own.

Water Drip Calculator
Even small, slow dripping leaks add up. Check out the Water Wiser Drip Calculator to find out how much water that little drip is really wasting.

Checking for Water Leaks
The best method for determining whether a leak exists is to take actual water meter readings. This method checks the entire internal plumbing system for water leaks.
  1. Take a water meter reading just before gong to bed or when no one will use any water for several hours.
  2. Take another meter reading in the morning before any water is used or after a few hours of non use.
  3. In theory, the two readings should be the same. If they are not and you cannot account for the use by a humidifier, ice cube maker, toilet flush, or water softener; you have a leak, and further investigation is recommended.
Toilet Tank Leaks
From our experience, 90% of the leaks in residential plumbing systems are found at the toilet tank (malfunctioning water softeners and humidifiers run a distant 2nd and 3rd). Toilets leak at the bottom of the tank around the flapper plug or at the top of the tank at the overflow tube.

Testing the Flapper Plug
To test the flapper plug, take the following steps:
  1. Carefully remove the lid from the toilet tank and mark the water level in the toilet tank with a pencil.
  2. Shut off the water supply to the toilet.
    • If the water remains on the mark you made for 10 minutes, the flapper plug is not leaking.
    • If the water level drops below the mark you made, the flapper plug is leaking and should be repaired or replaced.
Overflow Tube
The water level in the toilet tank should be at least 1 inch below the top of the overflow tube. If the water level in the tank is at the top of the overflow tube, that is where the leak may be occurring, and the float that controls the water level in the tank should be adjusted so that the water level in the tank is at least 1 inch below the top of the tube.

Reasons for Leaks & Making Repairs
Toilet tank leaks typically result from worn parts or misalignment of some part of the flushing mechanism. Most repairs can be done by an experienced do-it-yourself person. If you are not sure you can handle the job, call a plumber right away.


This article was reprinted from Outflow, Vol. 24, No. 4, April 1998, a publication of the American Water Works Association.