What is acoustic water leak detection, and how is it done?

Why does a leak make a sound?

The pressure in the water turns into turbulence as it escapes through a hole or a crack. Depending on the pipe material, diameter, pressure and ground, that turbulence radiates a continuous sound in roughly the 20–2,500 Hz range. In metal pipes the sound travels far; in plastic pipes (PE, PVC) it decays quickly, which is why measurement points are spaced more closely.

Step 1 — Preliminary zoning

The network map, valve positions and any DMA boundaries are reviewed. The area with high loss data is chosen as the priority zone to survey. If needed, the zone's minimum night flow is measured with a temporary flow logger.

Step 2 — Night survey with noise loggers

Noise loggers are placed on valves and hydrants. The devices record automatically during the quietest hours of the night; points that give a continuous, high-amplitude sound are flagged as "suspect". This step quickly screens a wide area.

Step 3 — Narrowing down with a ground microphone

Along the suspect main, point-by-point listening is done from the surface with a ground microphone. The sound level rises as you approach the leak; the location of the highest reading is the leak's surface projection. A listening rod is used on valves and connections.

Step 4 — Locating to the metre with a correlator

A sensor is placed on each contact point (valve, hydrant) on either side of the leak. Using the difference in arrival time of the leak sound at the two sensors and the speed of sound in the pipe, the correlator locates the leak between the two points to within a metre. When the pipe material and diameter are entered correctly, the margin of error is very small.

Step 5 — Confirmation and hand-over

The identified point is verified with the ground microphone; its coordinates and sound level are recorded and photographed. Excavation is done only for this confirmed point. All points are entered onto the GIS map and the LeakExpert platform.

Why work at night?

Daytime demand, traffic and ground noise mask the leak sound. When demand stops at night the network goes quiet; the leak sound becomes relatively distinct and is picked up from much farther away.

When is it not enough on its own?

On very deep mains, large-diameter transmission pipes, high groundwater and entirely plastic new networks, the acoustic method is used together with flow/pressure measurement and step testing. That is why LeakExpert relies not on a single method but on a closed-loop programme.

• Related service: Acoustic leak detection
• Concept: What is a DMA?
• In practice: Project pages