Water Leak Detection

Every drop of clean water is precious. Unfortunately, ~50% of clean 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.

Importance of Leak Detection

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 book-keeping, 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, pollutants 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 fire fighting services, park sprinkler and irrigation systems, city-owned pools and recreational facilities, etc. 

Leak Detection Methods

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. 

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. 

In addition to the direct loss of water, there is costly energy losses associated with municipal water loss as a result of pipeline leaks. 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. 

Emerging Leak Detection Technologies

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 re-establish 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.

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