Acoustic leak detection: what the equipment really hears

This page is about the technique rather than about a kind of leak. If you want the symptom-side explanation, start at slab leaks, buried lines or water mains. This is what the listening equipment is doing while it is on your floor.

The sound a leak makes

Water forced through a small opening in a pressurised pipe becomes turbulent, and turbulence is noise — a steady, broadband hiss rather than a drip. The pipe wall carries that hiss along its length far better than soil or concrete carries it upwards, which is the single most useful fact in the whole method: you can often hear a leak best somewhere it is not.

Two things follow. The loudest point on the ground is a strong candidate, not a verdict. And listening at a fitting that is connected to the pipe — a meter, a valve, a hose bib, a riser — tells you whether a leak exists on that run long before it tells you where.

What is actually in the case

Ground microphone

A weighted sensor placed on soil, concrete or tile, moved in a grid. It measures how loud the leak signal is at each point, and the pattern of those readings — rising towards one place and falling away on all sides — is what puts the mark down.

Contact probe

A rod that touches metal: the meter, a shut-off, a stub-out under a sink. Because it listens to the pipe rather than through the ground, it is the fastest way to answer “is this line leaking at all” before anyone starts crawling round a floor.

Correlator

Two sensors on the same pipe at known positions. The same leak noise arrives at each at slightly different times, and given the pipe material, diameter and distance between the sensors, that difference converts to a position along the run. It is the tool for a long buried run — a service line under a driveway, for instance — where there is nowhere useful to stand and listen in between.

What makes a property easy or hard to listen to

• Pressure. No pressure, no noise. This method only works on lines that are pressurised, which is one of several reasons we do not work on gravity systems at all.
• Pipe material. Copper and steel carry leak noise a long way. Plastic — PVC, CPVC, PEX — damps it, so a plastic line gives you less signal and a shorter range.
• What is on top. Concrete and tile transmit well but spread the signal sideways, so a leak under a slab or a driveway can read loudest a surprising distance from the break. Carpet and pad soak up the high frequencies that matter most.
• The ground itself. Caliche and saturated soil change what reaches the surface, and water that has already spread sideways along a hardpan layer is quieter than water still being forced through the hole.
• Background noise. Pool pumps, air-conditioning condensers, traffic, wind in a block wall and a neighbour’s irrigation all raise the floor you are trying to hear under. A quiet hour is worth more than a better microphone.

What acoustic detection cannot do

It cannot find an unpressurised leak. It cannot reliably separate two leaks on the same run until the louder one is fixed. It will not give a depth. A large, open break in soft ground can genuinely be quieter than a pinhole at full pressure, so loudness is not a measure of severity. And on a low pressure drip zone there is usually nothing audible at all, which is why drip leaks are found by running the system and reading it instead.

What we use instead, and when

Pressure testing to prove a line is losing at all. Thermal imaging where the leak is on a hot line under a readable surface. Dye tracing for the still water at a pool shell, where there is no pressure to make a sound. Line tracing to establish the route before a mark means anything. Acoustics answer one question well; they are cross-checked against at least one of the others before anything is opened — and before any leak repair starts.

Helping us hear

If you know we are coming to listen, switching off the pool pump, any water feature and the irrigation timer for the visit genuinely improves what we can hear. So does keeping dogs, music and the vacuum out of the way for an hour.