Acoustic leak detection questions answered

It is finding a hidden leak by listening for it. Water forced out of a pressurised pipe makes a hiss that travels through the pipe and the ground or floor around it. An engineer uses sensitive microphones and an amplifier to pick that sound up at the surface and follows it to the point where it is loudest.

The listening itself does no damage. The microphones sit on the surface or touch pipe fittings, though the engineer may lift an access hatch to listen closer. Once the leak is located, a small area is opened to reach the pipe, and the aim is to keep that to one spot.

Often, yes, but plastic pipe (the blue MDPE used for many supply pipes, and the plastic used in underfloor heating) carries sound less well than copper, lead or iron. The hiss fades faster, so the engineer listens at closer intervals and usually confirms the spot with a second method such as tracer gas before anything is opened.

Yes. A leak only makes a useful sound when water or air is being pushed out of it. Mains supply pipes are already under pressure. A heating system that has lost pressure may need topping up for the survey, and some pipes are pressurised with air so the escape can be heard. Drains and gutters are not under pressure, so listening is the wrong tool for them.

There is no single figure. How far the sound carries depends on the pressure, the size of the hole, the pipe material, how deep it is and what it is buried in. Compacted or wet ground, concrete and paving carry sound differently from loose soil. That is why the engineer compares levels along the whole route rather than trusting one reading.

A correlator places two sensors on a pipe, one at each end of a length, and measures the difference in the time the leak’s sound takes to reach each one. Knowing the pipe’s length and how fast sound travels along that material, it calculates where between the two points the leak is. It suits long runs of main where there is access to the pipe at both ends, which is why water companies use correlation on their networks.

Not usually. On most visits it is one of several methods. A pressure test proves there is a leak and which section it is on, listening narrows it down, and tracer gas or thermal imaging can confirm the spot. When two methods point at the same place, the engineer can open up with confidence.

Tell the office what you have noticed: meter readings, pressure loss, damp patches, or where you can hear water. On the day, the engineer may ask for taps, washing machines, dishwashers, pumps and other noisy appliances to be switched off while they listen, because every other sound in the pipework competes with the leak.

Background noise is the main one: traffic, pumps, running water elsewhere in the house, wind and rain. Thick carpet and underlay soften the sound on floors, and very small leaks may make little noise. Pipes that loop back on themselves, such as underfloor heating, can make a leak sound as if it is somewhere it is not. The engineer allows for these and uses another method where listening is not decisive.

ADI Leak Detection’s engineers work across England, Scotland and Wales. Call the office with your postcode and they will arrange a visit.

Yes, if you want it done. On many of the jobs on this site the engineer opened up the spot, replaced the damaged section and pressure tested the repair. What is possible depends on where the pipe is, so ask when you call.

Yes. ADI writes up what was tested, what was found and where, with photographs, in a report you can send to your insurer if you are making a claim.

If the survey shows the leak is outside your boundary or on the water company’s pipe, the engineer will tell you so you can report it to them. One customer on our reviews page was advised to contact the water company once the leak was found.