Underground water leaks can be detected using pipe tracing and using ground microphones. They can also be found by checking leaking noise correlation or using a tracer gas. Additionally, leaking pipes can be detected through pipe stopping for smooth bore pipes.
Pipe tracing involves adding a generator to metallic pipes. The generator then sends signals through pipe and a tuned receiver detects them. Alternatively, you can detect the sound of leaking pipes using microphones at the internal stopcock and the boundary stopcock. Leaking metal pipes tend to hiss at a higher pitch and louder than PVC and concrete pipes.
Using water detectors or ground microphones is a similar method. These microphones pick the sound produced by leaking water due to the pressure created.
A harmless and inert tracing gas that is 95 percent nitrogen and 5 percent hydrogen can be introduced into the pipes to check for leaky pipes. The hydrogen molecules in the gas escape from the pipes through the area that is leaking. This way, the leakage area can be detected using sensitive sensors.
Pipe stopping can also identify leaking pipes. This technique involves implanting a small airbag in the pipe, which is inflated to seal the pipe and air is allowed into the pipe. If the pipe does not leak, the pressure will hold. However, if the pressure reduces, there's a leak.