Every acoustic instrument does the same job in a different place: it picks up the hiss of escaping water and passes it to an amplifier and headphones. These are the instruments in ADI engineers’ own photos from real jobs.
Monday to Friday, 7:30am to 6:30pm. Tell the office where you think the leak is and they will book the right survey.
Also called a ground mic or surface microphone
A weighted metal cylinder, about the size of a tin of paint, often banded red and white or left bare silver. It sits flat on paving, tarmac, concrete or tiles and is moved on a long handle or a curly lead. A cable runs back to a handheld amplifier the engineer wears on a strap, and they listen through red ear-defender headphones.
The engineer follows the pipe route and puts the microphone down at regular stops, listening and noting the level at each one. As the levels rise, the stops get closer together until one point is clearly the loudest.
Traffic, wind, rain and running appliances compete with the leak. Plastic pipe, deep pipes, loose ground and carpet all soften the sound, so readings are compared along the route and checked with another method where needed.
Also called a contact probe or listening rod
A steel rod with a rubber grip at the top, plugged into the same amplifier and headphones. The tip is touched onto a stopcock, meter, valve, radiator tail or exposed length of pipe, or lowered into a stopcock chamber.
Leak noise travels along the wall of the pipe, especially metal pipe. Touching the rod on fittings at different points tells the engineer whether the leak is making a usable sound, and roughly which direction it is in.
It hears the pipe, not the ground above it, so it tells you the leak is on that pipe rather than exactly where along it. Plastic pipe carries the sound a much shorter distance.
Also called a contact sensor or floor sensor
A flat disc microphone, or a ground microphone on a three-legged metal foot, which sits steady on uneven or soft surfaces. Either one sits directly on a floor and picks up vibration through the surface. Engineers move it across a room in the same way as a ground microphone.
Placed on the floor over the likely pipe route, it picks up the leak sound carried through tiles, screed or boards. Readings in different spots are compared to find where the sound is strongest.
Thick carpet and underlay, floating floors and loops of pipe close together can blur where the sound is coming from.
An underwater microphone
A small waterproof sensor on a lead that is lowered into water: a pool, a skimmer pot or a tank.
Water carries sound well, so the hydrophone hears water being drawn out through a crack or a leaking fitting. Placing it at each skimmer and fitting in turn narrows down which part of the pool circuit is losing water.
Pumps and filters must be off while listening. Dye and pressure tests on each pipe line confirm what it hears.
The listening unit that every sensor plugs into
A handheld box, worn on a strap, with a small screen showing the signal level, a volume knob and a filter knob marked in frequency bands. Closed headphones shut out noise around the engineer.
It boosts the faint hiss from the sensor, and its adjustable filters cut out the frequencies where traffic and footsteps are loudest while keeping the band where the leak sounds clearest. The display shows a level for each stop, so the engineer compares numbers as well as what they hear.
Only as good as the conditions: filters help, but a quiet moment helps more.
A correlator uses two sensors placed on a pipe, one at each end of a length, often on valves or hydrants. Both send the sound they pick up to a processing unit, which works out the difference in the time the leak’s sound takes to reach each sensor.
Knowing the length of pipe between the sensors and how fast sound travels along that pipe material, the unit calculates where between them the leak must be. It needs access to the pipe at both ends and accurate pipe details, so it suits long runs of main, which is why water companies use it on their networks.
On most jobs the acoustic instruments work alongside other methods, and the strongest findings are where two of them agree.
A home swimming pool was losing water, and faster when the pump was running. A hydrophone in the skimmer pot picked up leak noise, and the investigation found a cracked skimmer body and a cracked glued joint in the filtration pipework.
Read the case
Water was coming up through tarmac at the front of a house. An acoustic listening device picked up a strong leak signal on the tarmac, and a single targeted dig exposed a leaking 25mm metal supply pipe, which was repaired the same visit.
Read the case
Booster pumps on a large park home site could not build pressure. Listening picked up the sound of water flowing in the site drains, which the engineer followed along three roads to an empty plot, where the leaking pipework was found and repaired.
Read the case