Understanding Leak Detection

Understanding Water Leak Locating

Leak location combines many factors in any given investigation.  Water leaks in underground pressurized pipes are commonly found using acoustic leak detection.  The principle behind acoustic leak location is that water leaving a pipe under pressure creates vibration and noise that can be detected on the surface.  The idea that the louder the noise the closer to the leak you are. 

Factors that affect these sounds and their intensity are:

  • Water pressure in the pipe
  • Pipe material and pipe diameter
  • Soil type and soil compaction
  • Depth of soil over the pipe
  • Surface cover: grass, loose soil, asphalt, concrete slab, etc.
  • Type of break on the line.

How Do Leak Sounds Travel Through Soil?

Soil absorbs water leak sounds very quickly:

Soil absorbs the high frequencies to a greater degree than the low frequencies. For a leak in a pipe 6 ft deep, the “Hiss” or the “Whoosh” sound is weak and “muted,” i.e. only the lower frequencies are heard. For a leak in a pipe 3 ft deep, the sound is louder and slightly higher in frequency.

To find this spot, the listener must carefully mark the location of the water line on the street after locating it exactly with a pipe and cable locator. Usually, the piping between the valve or hydrant with the loudest sound and the valve or hydrant with the second loudest sound is the section of the line that needs to be marked. The section must be accurately located and marked on the street in order for the listener to consistently listen directly over the pipe.

First:  Why do we suspect a leak? 

The first question helps us to make a determination if this is an actual leak situation or perhaps another cause or source of unexplained water.

  • Is there unexplained water on the surface of the ground?
    • Unexplained surface water could be the result of groundwater, Springs, or poor drainage. 
    • Surface water may be an indication of a leak if it is combined with one or more other symptoms such as a higher water bill.
  • Is the water chlorinated?
    •  The presence of Chlorinated can be a leak but it also could be a fault in a sewer line combined with faulty toilet or a running faucet.  
  • Is the meter showing higher than normal water usage?
    • This is usually a good indicator.  However other factors need to be considered.
      • A pool may need maintenance.
      • There may be a fault in an irrigation system.
      • Is a remote hose bib running or a toilet stuck in the running position?
        • A running faucet or a bad irrigation valve can waste hundreds of gallons a day.
  • Is the system holding pressure?
    • Fire lines should hold static pressure with no water usage. If there is a loss in pressure or a corresponding spike in usage not related to service, a leak may be present.
  • Is a jockey pump running continuously?
    • Jockey pumps are placed on fire systems to maintain pressure. A jockey pump should never have to run frequently.  This is a sign that the system is losing pressure.  

Second: Perform a utility locate.


Once a water leak is determined to be likely.  A utility locate should be performed to locate and understand the system.  Prints and as-builts or diagrams of the system are helpful in this process. Understanding the system in question helps the investigator develop a plan.  The investigator can eliminate areas that may not be of concern.  

  • The system should be mapped and surface features such as Hydrants, Meter Pits, Valves, and building risers should be noted on the map.
  • The types of materials and pipe diameters should also be noted if the information is available.
  • The approximate depth of the lines should be noted as well.

Third: A plan should be devised to begin the leak locate.

  • What method of leak location should be used?
    • There are two common methods of leak location.
      • Acoustic location- using sensitive listening equipment to locate the source of noise generated by pressurized water leaving a pipe.
      • Helium location- Introduce helium into the water line and use sensors on the surface to detect the helium as it escapes the soil above the leak.
    • If possible, Isolate portions of larger systems to narrow down or eliminate portions of the system.  This saves time and money. 

Fourth: Begin investigation

Find the waterline in question to pinpoint the leak.

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