Leak Detection, Locating, Correlating and Logging – What's the Difference?

A variety of tools can be used to identify and limit water loss. Knowing the differences – and how they are deployed – is key

Leak Detection, Locating, Correlating and Logging – What's the Difference?

A technician from New York Leak Detection uses the Investigator from JD7 to do a live insertion for internal condition assessment and leak detection at a New Jersey site. (JD7 photo)

There are a number of different technologies and tools that can be used for water loss management in a water utility. Each has it's advantages and limitations. A utility can and should use more than one in most cases, but should at least have some technology to proactively detect and locate leaks. Just as your doctor might use an X-Ray, a CT Scan machine, ultrasound or MRI to find hidden flaws in your own body, a water utility can use a number of different technologies to find flaws in your water distribution system, with certain pieces of equipment performing a slightly different method or working  better in a different situation or different size utilities. Below I'll discuss a few of them and what they offer. The overall goal of all of them is normally referred to  as Water Loss Management, or "WLM".

Leak Detection - Leak detection is the very simplest form of WLM. It is just discovering that there is in fact a leak. You can't fix a problem until you know you have one. Passive leak detection would be just sitting back and waiting for the public or your staff to report water coming up where it shouldn't. Hopefully, your utility is a bit more proactive and has a plan to detect leaks that may not come up or be reported immediately. Not all leaks will be evident on the surface, as they may leak into streams and rivers, back into ground or aquifer, or into storm or sanitary sewers unseen.

One form of leak detection is just comparing the amount of water produced to the amount of water sold through metering to come up with a figure for "non-revenue water". A portion of non-revenue water will commonly be used for fire protection or due to inaccurate metering, but if the difference is large or starts to rise, that would also be a form of detecting that you have leaks developing somewhere in your system. Now you need to find where they are to fix them. Very simple leak detectors can be used to listen to a water line at hydrants, valves or meters to listen for leak noise. This again can tell you you have a leak, but does not necessarily pinpoint the leak for repair. That's where you need equipment to physically locate the problem.

Gary May, a GIS Field Technician with the Henry County Water and Sewer Authority in Georgia, uses an Fluid Conservation Systems Lmic with probe to listen for leaks at fire hydrant. (David Makkers photo)
Gary May, a GIS Field Technician with the Henry County Water and Sewer Authority in Georgia, uses an Fluid Conservation Systems Lmic with probe to listen for leaks at fire hydrant. (David Makkers photo)


Leak Locators - Leak locators can be simple or technically sophisticated, but are tools to help you find the LOCATION of known or unknown leaks in the distribution system in order to repair them. Water doesn't always come up exactly where the leak is located, particularly when under pavement. A combination audio leak detector/leak locator can be used to detect the sound of leaks on a water main at access points, then follow the lines on the ground above the pipe to hone in on the maximum sound as a leak locator. 

Leak locators normally put some numeric value to leak noise so that you know when you are getting closer to the leak. Leak locators can be very simple analog devices with no more than a ground microphone and earpiece. Better leak locators will have high-end leak noise sensors with digital audio processors that can filter out background sound and loud noises. This helps the utility worker more accurately differentiate leak from non-leak  sounds even in noisy environments, and even detect what type of leak it is  such as a main leak versus a service line, or a pinhole versus a large crack. A limitation of devices  used to locate to leak noise from the ground over the pipe is that you must know where the pipe is underground to listen on top of it. A utility should either have accurate GIS, maps, markings or a pipe locator as well. These locators often called ground microphones can be very accurate in most circumstances, but can take some time to use listing down the line.

Operations manager Richard McDaniel of the Rockdale County Water Resource in Conyers, Ga., uses 370 Permalog+ acoustic leak noise loggers, a Patroller II drive-by data collection device, a TriCorr Touch real-time leak noise correlator, a SoundSens “i” advanced correlating logger system and an Xmic ground microphone from Fluid Conservation Systems to analyze leak noise from water lines, transmit the data to mobile collection units, and pinpoint leaks to minimize repair time and cost. (Photo courtesy Fluid Conservation Systems)
Operations manager Richard McDaniel of the Rockdale County Water Resource in Conyers, Ga., uses 370 Permalog+ acoustic leak noise loggers, a Patroller II drive-by data collection device, a TriCorr Touch real-time leak noise correlator, a SoundSens “i” advanced correlating logger system and an Xmic ground microphone from Fluid Conservation Systems to analyze leak noise from water lines, transmit the data to mobile collection units, and pinpoint leaks to minimize repair time and cost. (Photo courtesy Fluid Conservation Systems)


Leak Noise Correlators - A  leak noise correlator can be used to mathematically determine where a leak is located between two leak sensors, and can quickly and precisely pinpoint a leak. Leak sound will travel down the pipe wall away from the leak. Engineers have determined the normal speed of sound through different sizes and materials of pipe. These speeds are programmed into software so that a mathematical formula is used to determine the time difference leak noise takes to reach two or more sensors from the point of the leak. Three things are generally needed to do the calculations which include the pipe material, pipe diameter, and the footage of pipe between  the sensors. With these inputs, the  software can accurately calculate the distance of the leak from each sensor. 

Leak correlators can give very accurate leak locations to pinpoint leaks for repair, and can often  even find multiple leaks in the distance between the sensors at one time even though a person may only hear the louder one with a simpler leak locator. A best practice is to verify the correlation by verifying the location with a ground microphone in case of errors in the data entered to do the leak noise correlation. 

Leak Loggers - So far, all of the items above are discussed as being used live in the field by a person. However, many leaks are difficult to find in daytime hours due to traffic, daytime noise of everyday use of the water system, lower system pressures due to use, and other factors. Leak loggers take leak detection and locating to the next step by being able to log leak sound without a utility worker present, which could be at night, on weekends. Logging can also be used to take repeated leak noise recordings over time to determine  if a leak is growing, developing, or to rule out short term usage that could  be falsely detected as leak. Leak loggers can record leak sound at a single location like a simple leak detector. Leak correlators that can be set to log and  correlate at the same time can also be used. 

Another type of leak logger is permanent or semi-permanent. These loggers can be installed in quantities of a few or even thousands in valve boxes and left for a week or two survey and monitor an area, or on a permanent basis throughout the distribution system. When permanently installed, and read with a drive-by system, they are proactively monitoring for new leaks 365 days a year. They can catch leaks when they start small, reducing the total water lost before being detected and repaired. Since many leaks start small and grow over time, they can often leak for weeks or months before actually being detected visually. Since smaller leaks are cheaper the utility can save on lost water, repair parts, and the labor required for large repairs and property and road restoration.

A technician in Chula Vista, California, uses PipeLogix pipeline assessment software to collect CCTV survey data, which is then imported into an ESRI ArcGIS mapping program. It is used to help plan upcoming inspections, and pull data into the city’s core software, Lucity, which handles asset inventory, maintenance management and GIS compatibility. Pipelogix’s PACP-rated asset data us used to determine which lines get rehabilitated or replaced, and in planning new development. (Pipelogix photo)
A technician in Chula Vista, California, uses PipeLogix pipeline assessment software to collect CCTV survey data, which is then imported into an ESRI ArcGIS mapping program. It is used to help plan upcoming inspections, and pull data into the city’s core software, Lucity, which handles asset inventory, maintenance management and GIS compatibility. Pipelogix’s PACP-rated asset data us used to determine which lines get rehabilitated or replaced, and in planning new development. (Pipelogix photo)


Leak Mapping - This is a newer concept of recording the location and other data from leaks in geographical format, typically integrating with GIS systems or a geo-database. This can build an information database on leaks and water losses to predict weak areas for leak surveying, plan pipe replacement and rehabilitation, cost justify line replacement for budgets and grants, and begin to learn what may cause certain types of leaks in different areas or different types of pipes. Keeping a history of leaks and repairs can be valuable information in managing a water system and planning to prevent future losses.

Mapping leaks allows visualization of the system leak history as a whole. Data for a leak mapping system can come from work order systems, manual entry, or data logged from many different types of leak locating and logging devices. Sophisticated Water Loss Analytics software can also be used for combining water production and distribution data from a SCADA system, water consumption data from an AMR or AMI metering system, and pipe and logger location data from GIS or other mapping sources.

Whether your utility has 100 users or 1 million users, there is a technology that will fit your budget to reduce your non-revenue water loss.

Mark Beatty is CEO and Principal Owner at Utility Technologies, LLC. This article was originally posted on LinkedIn, and is being used with Mark's permission.



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