Companies that make underground water leak detectors include Fisher, Metrotech, SPX and Amprobe. These devices detect leaks using a variation of acoustic, ultrasonic and tracer-gas detection methods.
Water leak detectors identify leaks using the acoustic sounds generated by water escaping a compromised pipe. The sound heard at the ground surface based on the properties of the pipe, its depth from the surface, and the type of material covering the pipe.
A basic acoustic leak detector uses a microphone, placed either at the ground surface or a water service line, to amplify sounds within the normal range of human hearing. For sounds that are beyond human hearing, ultrasonic leak detectors are best as they are able to detect high-frequency sounds. The tracer-gas method uses non-reactive helium gas and is well-suited for detecting leaks within closed systems.