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 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.