Last reviewed and updated: 2026-09-24
Acoustic leak detection locates pressurized water leaks by listening for the sound they make. Water forced through a small opening produces a continuous high-frequency hiss that travels along the pipe wall and through surrounding soil and concrete. Ground microphones amplify that sound at the surface, and leak correlators use sensors at two points on the line to calculate the leak's distance from the time difference between the signals.
Acoustic listening is the first method reached for on a slab leak or a buried service line. Where the pipe is plastic, too quiet, or unpressurized, it hands over to tracer gas or a drain camera.
How it works
A leak on a pressurized line is a continuous noise source. The sound radiates in two directions along the pipe wall and outward through the surrounding material. Two instruments exploit this.
Ground microphones are highly sensitive contact microphones placed on the surface above the suspected line. The technician works along the traced route; the signal amplitude peaks directly above the leak. This is what locates a slab leak through concrete.
Leak correlators use two sensors clamped to accessible points on the same line, typically the meter and a hose bib. The leak noise reaches each sensor at a slightly different time. Given the pipe material, diameter and the distance between sensors, the correlator calculates exactly where along the run the leak sits. This is how buried service line leaks are found without digging exploratory holes.
Where it works well, and where it does not
| Condition | Effect on acoustic detection |
|---|---|
| Metal pipe (copper, galvanized, cast iron) | Excellent: metal carries leak sound efficiently over long distances |
| Plastic pipe (PVC, PEX, polybutylene) | Harder: plastic damps the signal, so listening range is much shorter |
| High water pressure | Helps: more pressure means a louder leak |
| Very small leak or low pressure | Difficult: may need tracer gas instead |
| Concrete slab | Works well: concrete transmits the sound to the surface |
| Deep burial or loose fill | Harder: the signal attenuates through soil |
| Background noise (traffic, appliances, wind) | Reduces accuracy, which is why surveys are often done at night |
| Drain and sewer lines | Does not work: unpressurized lines make no continuous leak sound |
Why quiet matters. The technician is listening for a faint hiss through concrete or soil. A running refrigerator, an HVAC unit cycling, or traffic outside all compete with it. Turning appliances off during the survey genuinely improves accuracy.
What it is used alongside
Acoustic detection rarely works alone. Pressure testing establishes which line is losing before anyone listens, line tracing establishes where to listen, and thermal imaging or tracer gas confirms the location before anything is opened. A single acoustic peak is a strong indication; a peak confirmed by a second method is what justifies cutting concrete.
Frequently asked questions
What is acoustic leak detection?
A method of locating pressurized water leaks by listening for the continuous high-frequency sound water makes escaping through a small opening. Ground microphones amplify that sound at the surface, and correlators calculate the leak's position from the time difference between two sensors on the line.
Does acoustic detection work on plastic pipe?
Less well than on metal. Plastic damps the leak sound, so the effective listening range is much shorter. It still works, but it usually needs to be combined with more precise line tracing and often confirmed with tracer gas.
Why does the technician want the house quiet?
Because the target sound is a faint hiss traveling through concrete or soil. Refrigerators, HVAC units, washing machines and traffic all produce competing noise. A quiet house measurably improves the accuracy of the location.
Can acoustic equipment find a sewer or drain leak?
No. Drain lines are not pressurized, so they produce no continuous leak sound. Drain leaks are found with camera inspection, smoke testing, dye testing and hydrostatic testing instead.
How accurate is it?
In good conditions on metal pipe, a leak can be narrowed to within inches. Accuracy falls with plastic pipe, deep burial, low pressure, very small leaks and background noise, which is why a second confirming method is used before anything is opened.