Successful Water Leak Detection and Audit Methods

Dec. 7, 2017

Every drop of clean water is precious. Unfortunately, 30–50% of water is lost through aging infrastructure. And lost water equals lost revenue to the water service supplier. Water is lost through leaks and cracks in pipes and their fit­tings. Since most infrastructure is underground, it is virtually impossible to visually determine the location of these leaks unless the water has reached the surface (causing ponding and sink holes, structural damage, buckling pavement, etc.), and the exact location may be indeterminate. Leak detection requires special technologies that allow inspectors to precisely determine the location and severity of pipeline leaks. This is a field that continues to grow and advance by utilizing both established technology and by adopting emerging methods.

Water lost through leaks, waste, or simple theft is referred to as non-revenue water, in that it fails to provide revenue to the water supplier because it never reaches its customers. These can be physical losses of water escaping the system, or unaccounted-for water that is not measured due to faulty meters and meters that have been tampered with, poor accounting and bookkeeping, or as a result of human error when reading and recording the water system flow meters. Available and emerging technologies are designed to detect and prevent physical water losses. These will continue over time until they are detected. The accumulation of losses over long durations can result in signi­ficant losses even from insignificant leaks. And if water can get out, impurities (soil, bacteria, organics, etc.) can get in and impair the quality of the water, even rendering it unfit to drink.

Non-revenue water losses are quantified the same way as water provided—volume (gallons or liters) per units of time (per minute for the actual leakage/flow rate or per year to measure accumulative losses). Water losses can also be measured in large water supply systems in terms of volume of water lost per the total length (miles or kilometers) of the pipelines that make up the water supply system. These values are then compared to the water supply flow rates to determine the percent of total water being lost or otherwise unaccounted for. As a general rule, water losses will vary proportionally with the age of the water supply system, or the ages of the various subsections of large metropolitan systems. Larger, older cities can have sections less than a decade old or older than a century.

Since the city operating a water supply system can be its own customer, certain water flows are considered to be accounted for but non-revenue in the sense that the city does not charge itself for water usage. These applications include firefighting services, park sprinkler and irrigation systems, city-owned pools and recreational facilities, etc.

Acoustic detection remains the primary means of detecting and locating pipeline leaks. The method of acoustic leak detection is described as “the systematic method of using listening equipment to survey the distribution system, identify leak sounds, and pinpoint the exact locations of hidden underground leaks.” Water escaping under high pressure from a pipe leak or crack makes a distinct rushing or hissing sound that can carry considerable distance along the length of the pipe itself (in contrast, the loose soil surrounding the pipe in its backfilled trench makes a poor conductor of sound). In this sense, the pipe acts as a medium for transmitting sound. In doing so, it can act like the strings on a guitar, vibrating with different pitches for different pipe lengths, diameters, and materials. Small diameter metal pipes carry sound the greatest distance, up to 1,000 linear feet, while large diameter polyvinyl chloride (PVC) pipes can carry sound only 100 feet.

The listening devices used to detect this sound come in various operational modes. They can be mobile or fixed, direct or indirect, external or internal, or transit data via radio or utilize manual download into laptop computers. There are mobile acoustic sensors that are manually operated or run along the pipe segment on wheels. In either case, the sensors consist of ground microphones that listen below the surface as the operator walks along the pipe segment. As he operates his sensor, the signal will get louder as he zeroes in on its location. There are also permanently mounted units in fixed locations along the pipe network. Accuracy is typically between 3–4 feet—more than sufficient to allow digging operations to expose and repair the leak. The use of mobile devices can be hampered by local environment and engineered structures. Sound at the surface can be muffled by deep soil, thick roadway pavement, or heavy local traffic.

A leak detection device in operation

Secondary leak detection methods utilize pressure differences. These are measured by strategically located flow meters and pressure gauges that can, by differences in the readings, bracket the location of the leak. For example, if flow rates at the start of the pipe length are significantly higher than at its terminus, it is likely that there is a leak occurring between these two points. Pressure drops compared to initial operating condition immediately after installation will indicate the escape of water and subsequent lowering of pressure from its original state. The two systems can be used together with the pressure and flow differentials used to bracket the leak’s location and mobile acoustic sensors running along this bracketed length to pinpoint its location. The use of the former saves considerable time and tedious effort by the latter.

A leak detection usage chart

In addition to the direct loss of water, there are costly energy losses associated with municipal water loss as a result of pipeline leaks. As a single service category, municipal water utilities are the largest user of electricity in the US (Source: Von Sacken, 2001). All that electrical power is for naught if the pumped water ends up spilling out of the system. The damage done to adjacent infrastructure is another significant, if indirect, cost. Old, damaged infrastructure (shifting and dislocating pipelines, roadway potholes, shifting and sinking structural foundations, etc.) is a financial time bomb.

Leak detection is just the first step. To minimize leakage loss, a water supply system must have a program of continuous audits, of which leak detection is just a part. A full-scale audit program should be performed at least annually with complete analysis of the leak data—not just for the current audit, but accumulated data records over time. A proper audit examines the accuracy and completeness of the system’s entire leakage database. This data does not just include reading on the leaks themselves, but also indirect measurements of potential leaks such as customer billing and receipts, along with flow meter and pressure gauge readings.

Though typically represented in a tabular format, audit data becomes most useful when portrayed geographically with data superimposed on maps of the water system that is being audited. This visual representation makes it easy to identify and isolate problem spots where leaks may be occurring. Graphically, pressure readings can be used to create pseudo-hydrostatic contours representing areas of low and high pressure. Low pressure zones thus revealed are another danger sign that a leak may be occurring in these areas. Similarly, flow measurements as represented by two-dimensional graphs (with flow rates represented by the y axis and pipe segment length shown by the x axis) can also show potential leak points.

Audits are typically costed by the mile, and they are not cheap (especially for large water supply systems). But they are essential and are far less expensive than continued water loss. Audits provide update information on system performance, tagging what is failing and (more importantly) highlighting those areas that are functioning properly. This is important with regard to evaluating previous maintenance and repair operations prompted by the results of previous audits. In short, a water system audit provides its own information feedback loop. As a side benefit to the audits, complete inventories of the water system’s equipment, valves, and fittings can be collated.

In this age of automation, many tasks still require the hands-on touch of human operators. A water leakage audit is one such task. The easiest time to perform those audits is during off-peak hours (such as the very early morning). With most people asleep at these hours, water usage should be relatively flat. However, if water distribution actually increases, it is a clear indication that leaks are occurring in the pipe system. Since this initial measurement only lets the operator know that leaks are occurring (but not much else), it represents only a preliminary step.

The next step is to identify all potential sources of water feeding into the water supply system and sum up their measured flow rates (gallons per day). This gives the baseline value for the amount of water that should be flowing through the system and through each pipeline network subsection. Next, flow meter readings should be tallied up. This provides hard field data (adjusted for potential meter error) on actual water usage flow rates. Then water flows entering the system can be compared with water usage exiting the system to determine the gross magnitude of water leakage.

After this amount is determined, the audit can break down water usage by individual customers (residents, businesses, commercial and industrial facilities, rental units, etc.). This involves both a thorough review of the data from the last year’s audit and the meter readings over the past year. Increases in flow rates indicate that the customer has either increased its usage due to expanded operations and increased economic activity, or that the customer itself has unreported leaks. If the latter is the case, it is up to the customer to find and repair any leaks that are occurring on his side of the flow meter. The water utility is only responsible for leaks on the street side of the meter.

With each pipe segment of the water distribution system defined by flow and pressure monitoring points, both the approximate location and amount of water being lost at a leak can be determined. The manual detection can then proceed to find the precise location of the water loss. The kind of leaks can vary considerably and can include illegal water taps, broken and malfunctioning meters, leaking pipe fittings and fixtures, and worn out valves. In addition to pipeline leaks, leaks can occur in water storage structures such as water towers, storage tanks, and reservoirs.

Lastly, a thorough review of the data and associated paperwork needs to be performed. In many cases, water losses are not physical losses. Instead, they are the result of poor bookkeeping and sloppy data entry. Since this is a problem caused by human error, human review and reentry of the data is necessary for correction.

Detecting leaks within a customer’s facility is not so much a matter of visibility, but of vigilance and continuous monitoring. New technologies are emerging that allow customers to pinpoint leaks within their facilities with a higher degree of accuracy than the traditional methods of water leak detection such as spot detectors, which detect leaks at a single point (such as a curbed area under a piece of equipment). Though economical and easy to use, spot detectors can only detect accumulated water in contained or low points. Water that doesn’t touch the spot detector’s probes will not be detected. An improvement on this system utilizes non-conductive sensing wire (which avoids shorting out if it comes into contact with metal surface or projections) and can detect any fluid, not just water.

Intelligent cable sensors are just one area of technological development. Each new advance will have to be rigorously evaluated for general usefulness and specific applicability. The factors used to evaluate new technology include: breadth of application and how many uses it can be applied to; ability to adjust sensitivity to different liquid amounts; the ability to quickly reset its readings and reestablish its sensing operations; ease of installation; scalability and adjustment to future expansions; and ease of integration into the existing control and monitoring system. Future technological advances must pass all of these hurdles to find acceptance among both customers and utilities.

Hermann Sewerin GmbH manufactures electro-acoustic water leak detection devices, noise loggers, correlators, tracer gas, and flow analysis equipment. Their Aquaphone A50 is a reasonably priced entry-level model for professional acoustic water leak detection. Its A50 receiver, UM 50 microphones, and TS 50 test rod allow for easy pre-location and pinpointing of leaks. Compact and easy to carry, when equipped with digital radio it avoids cables that can restrict movement. In addition to spot checking for leaks, their SePem noise data logger allows for continuous monitoring. The SePem 155 is designed for permanent use; they are magnetically attached to valve rod extensions, hydrants, or other metal fittings. The SePem 155 is designed for mobile use and temporary installation at key points along specified sections of pipe networks. More specific measurements are carried out by the AquaTest T10 test rod. This is used on objects that lie deep under the ground surface with easily screwed-on extensions for greater reach. It displays current noise levels, previous noise levels, and current noise intensity visually on a digital screen in the form of bar graphs.

A leak alert

One of the company’s newest products is the SeCorrPhon AC 200, a multifunctional leak detector offering three functions in one: pre-location, pinpointing, and correlation. Combining these functions allows an operator to locate leaks regardless of the ambient conditions. Designed for easy operation, the operator can quickly switch between the various applications. The vibrations made by leaks can travel through the ground up to the earth’s surface as ground-borne noise, albeit heavily muted.

The system assists in leak detection by making the vibrations audible to the human ear and also records and displays the volume and frequency spectrum as a graph. The operator places the carrying rod and the connected touch microphone on fittings along the pipeline and evaluates the volume. By evaluating the noise intensity, the operator can identify the section of pipeline where the leak is likely to be. The operator can pinpoint the volumes in the identified section of pipe using the BM200 ground microphone (for paved surfaces) or BM230 (for unpaved surfaces). The operator does so by connecting the carrying rod to a ground microphone and moving over the pipeline in short intervals. The acoustic signal and the visual display of the intensity make it easy to find the maximum. The leak is then located with sufficient accuracy to allow confident excavation.

The visual display on the user interface is clearly and logically laid out with many extra functions available for complex location scenarios. With acoustic leak detection, the current sound intensity is displayed as a graph and as a numeric value on the large and clear 5.7-inch receiver display. The previous values are displayed alongside for better comparison as well as the current frequency analysis of the noise.

The high-quality piezo microphones, with frequency response optimized especially for leak detection and the digital signal processing, offer outstanding acoustic properties. At the touch of a button, the system will apply tailored filters to the current noises and will automatically select the appropriate frequency ranges. Alternatively, the operator can set manual filter limits according to his individual hearing and select frequency ranges which accentuate the leak noise. This allows the operator to concentrate fully on the leak without any sound interference.

A companion instrument is the equally new SeCorr C 200, a state-of-the-art, portable, high-performance correlator, which enables leaks in underground pipelines to be located reliably, quickly, and accurately. The SeCorr C 200 is recommended for all users undertaking professional leak detection because it can handle any everyday location scenario. It can easily measure different pipe sections, pipe materials, diameters, and pipe lengths. The measurement sequence is almost fully automatic.

Once the pipeline data has been entered and the measurement started, all other steps are performed without the intervention of the operator. The measured noises are constantly analyzed in the background and the optimal filter settings selected. The on-screen display shows concrete information about the position of the leak instead of having to interpret complex curves. The calculations shown in the display provide the user with constant information. The SeCorr C 200 is certified to IP67 and therefore ideal for use in extreme ambient conditions. Dirt, dust, and moisture will not affect its functionality. The powerful integrated lithium-ion rechargeable battery means the receiver can be used all day long without interruption. It is also lightweight and ergonomic, further adding to its ease of use.

WaterSignal measures water flow in real time, allowing for fast detection of leaks and water conservation. The system allows Portfolio managers to login with any internet-accessible device and see a centralized dashboard of current water consumption across all sections of the water supply system. Its unique hourly and daily alert levels warn managers about excessive losses and prevent subsequent high billings. This real-time water use reading is far more efficient than standard monthly meter readings. The WaterSignal technology is directly installed on a water meter and then proceeds to manually calibrate the device to ensure accuracy. Data is then acquired continuously in real time and uploaded to a secure data center. The accumulated water use data is available to operators 24/7 through any internet device (iPhone, iPad, laptop, etc.). A sudden spike in water flow, indicating a catastrophic leak, will result in alerts being sent to the operators via email and SMS text message. The alert will include specific data indicating which water line has broken and how much water has been lost. This system has been used successfully in a number of commercial and public applications.

  • In 2015, WaterSignal installed a device in Miami, FL, to monitor the main domestic water line servicing 1050 and 1060 Brickell Avenue. The Brickell is a two-tower condo development featuring 576 contemporary condos. Later that August, WaterSignal detected that water usage had exceeded the alert level by 7,500 gallons. Prior to the installation of WaterSignal less than two weeks earlier, the Brickell Avenue site had been experiencing unexplained water bill increases but had no way to monitor and analyze water use. Had the leak remained undetected, the property would have paid an additional $19,000/week (based on local water/sewer rate of $11.37/1000 gallons). The source was quickly discovered to be a catastrophic leak from the cooling tower make-up line, allowing water to continuously flow into the parking garage.
  • In 2012, WaterSignal installed devices to monitor the main domestic water meter and fire line at Heathermoor Apartments in Columbus, OH, which included 280 updated apartment homes. By January, the property was exceeding the usage benchmark by 30,000 gallons daily. Due to WaterSignal’s real-time water monitoring, it was discovered that water usage had greatly increased over a period of time. Had the leaks remained undetected, the property would have continued to pay an additional $1,125/week.
  • In 2016, WaterSignal installed a device to monitor the irrigation meter for a corporate office building in Sugar Land, TX. This office park featured 176,000 square feet of premier commercial office space, and the irrigation water was used to maintain a green landscape. Two weeks after installation, WaterSignal alerted the property to excessive usage on the irrigation meter (something the owner has no way of knowing prior to using WaterSignal). WaterSignal was able to provide building managers with comparable water data, allowing them to see an irrigation leak that was causing 1.5 million gallons over the property’s monthly average. 
About the Author

Daniel P. Duffy

Daniel P. Duffy, P.E., writes frequently on the topics of landfills and the environment.