How does listening find the position?

The sound is loudest at the leak and falls away in both directions, so a listener comparing several points along the run can work out where the peak is. On a longer buried run two sensors are used at once, and the position is worked out from the tiny difference in when the same sound reaches each of them.

Why does plastic pipe make it harder?

Because the sound has to travel through the pipe wall to be heard from anywhere except directly above the leak, and a rigid pipe carries it further than a flexible one. A plastic supply pipe damps the noise over a shorter distance, so there are fewer places it can be heard from, and the listening has to be done closer to the leak that nobody has located yet.

Will it work if my leak is very small?

It may not. The noise comes from water being forced through a small opening, so a very slow loss makes very little of it. That is the awkward case: the leak is real, the meter has measured it, and there may not be enough sound to find it by listening.

Does noise around the house matter?

Yes, and more than people expect. Traffic, a pump, a fridge, rain on the ground and wind all sit in the same range as the sounds being listened for. It is why surveys are often done at night, and why it is worth mentioning a noisy road or a neighbouring site when you book rather than on the day.

Can I do this myself with a stethoscope or a phone app?

Not usefully. The problem is not amplification, it is separating one faint continuous sound from everything else at the same pitch, which is what the equipment and the operator are actually for. You are better off spending the effort on the stop tap test, which costs nothing and narrows the area more than an untrained listen will.

Acoustic leak detection, and when it does not work

Water forced out of a pressurised pipe makes a noise, and that noise travels along the pipe and up through the ground. Acoustic detection is listening for it, at the surface and at contact points like stop taps and meters, to work out where along the pipe it is loudest. It needs three things to be true: the pipe has to be under pressure, the site has to be quiet enough, and the pipe has to carry the sound. Plastic pipe carries it far less well than metal, which is the commonest reason the method struggles on a modern supply.

Last reviewed 14 August 2026

The short answer

It listens for the sound escaping water makes, and it works when the pipe is under pressure, the pipe carries sound well, and the site is quiet.

Those three conditions are the whole method. Everywhere it fails, it is because one of them is not true, which means you can usually predict how hard your property will be before anybody comes to look at it.

How this works in practice

Water under pressure escaping through a small opening makes a continuous hissing or rushing noise. That sound does two things, and both are used.

It travels along the pipe itself, in both directions, so it can be heard at contact points some distance from the leak: a stop tap, a meter chamber, an exposed length of pipe.
It travels up through the ground above the leak, so it can be heard at the surface, loudest directly over it.

A survey uses both. Contact points establish which stretch of pipe the sound is present in, then listening at the surface across that stretch narrows it to a position. On a long buried run, two sensors placed at either end pick up the same sound at fractionally different times, and that difference gives the position along the pipe.

Notice what is being located: the loudest point. That is normally the leak, and the method assumes it is. A second leak, a fitting that rattles, or a sound that carries better in one direction than the other all bear on that assumption, which is why a survey narrows to a position rather than marking a spot.

What changes the answer

Four things, and all four are facts about your property rather than about the equipment, so you can check them yourself before booking anything.

Condition	Why it matters	How to check
A plastic supply pipe	The sound travels a shorter distance along the pipe, so there are fewer points it can be heard from.	Look at the pipe where it enters the property, usually at the internal stop tap. Blue plastic is a modern supply; metal is older.
A noisy site	Traffic, pumps, appliances, wind and rain sit in the same range as the leak sound.	Stand outside at the time a survey would happen and listen. If you can hear a main road, say so when you book.
A very slow loss	The noise comes from water being forced through a small opening. Less flow means less sound.	Your measured rate of loss. A very low figure is a harder acoustic job, not an easier one.
A pipe not under pressure	There is no noise at all without pressure driving the water out.	This is why a heating circuit, a drain or a pool return is a different job from a mains supply pipe.

What makes acoustic detection hard

The third row is the one that surprises people, because it inverts the usual expectation. A big leak is loud and easy to find. A small leak is quiet and hard. So the cases where the meter test result is least alarming can be the ones where locating it costs the most effort, and it is worth knowing that before rather than after.

Where the pipe cannot be listened to at all, because it is plastic, silent, or not under pressure, the usual alternative works on a completely different principle. how tracer gas reaches what acoustic cannot explains what it needs instead.

Assumptions and sources

Drip Calculator: how much water does a leaking faucet waste?

United States Geological Survey, Water Science School · primary source

Faucet drip volume, adopted: 0.25 ml
Faucet drip volume, measured range: 0.2 to 0.33 ml
Bath tap drip volume: 0.5 ml
Drips per US gallon: 15140 drips
Drips per litre: 4000 drips

The pharmacopoeial metric drop, 20 drops to 1 millilitre

United States Pharmacopeia, British Pharmacopoeia and European Pharmacopoeia convention · primary-standard source

Standard drop volume: 0.05 ml

Tate's law: the weight of a falling drop

Thomas Tate, Philosophical Magazine, 1864, with the later drop-weight literature · primary source

Drop weight: W = 2 * pi * r * gamma equation

Plumbers shine the spotlight on dripping taps during Water Saving Week

WaterSafe, with Waterwise · untraceable source

Claimed annual waste from a dripping tap: 5500 litres per year

OIML R 49-1, Water meters for cold potable water and hot water, Part 1: Metrological and technical requirements

International Organization of Legal Metrology · primary-standard source

MPE, accuracy class 2, lower zone Q1 to Q2: 5 %
MPE, accuracy class 2, upper zone Q2 to Q4: 2 %
MPE, accuracy class 1, lower zone: 3 %
MPE, accuracy class 1, upper zone: 1 %
In-service MPE multiplier: 2 ratio
Q2 / Q1: 1.6 ratio
Q4 / Q3: 1.25 ratio

Aquadis+ DN15 and DN20 specification sheet

Itron · manufacturer source

Q1 minimum flow rate, DN15, Q3 2.5, R160: 15.6 l/h
Q2 transitional flow rate, DN15, Q3 2.5, R160: 25 l/h
Q3 permanent flow rate, DN15: 2500 l/h
Typical starting flow rate, DN15: 0.4 l/h
Typical starting flow rate, DN20: 2 l/h
Q1 minimum flow rate, DN20, Q3 4.0, R160: 25 l/h
Flow rate at which accuracy is within +/- 5%, DN15: 3 l/h
Flow rate at which accuracy is within +/- 2%, DN15: 5 l/h
Minimum scale interval, DN15 and DN20: 0.02 l

Water resources 2024 to 2025: analysis of the water industry's annual water resources performance

Environment Agency · primary source

Household per capita consumption: 136.5 l/person/day
Household per capita consumption, prior year: 137 l/person/day
Household per capita consumption, dry-year adjusted: 140.3 l/person/day
National leakage: 2617 Ml/day
National leakage as share of water put into supply: 19 %

PR24 common performance commitments: per capita consumption (PCC), version 2.1

Ofwat · primary-standard source

PCC formula: (measured household consumption + unmeasured household consumption) / total household population l/person/day

Leaky loos, why it's not as simple as faulty flush valves

ech2o, reporting research attributed to Thames Water · secondary source

Toilets inspected: 58551 toilets
Toilets found leaking: 4854 toilets
Prevalence: 8.3 %
Average residential leak rate: 400 l/day
Average commercial leak rate: 2100 l/day
UK-wide average across all WCs, leaking and sound: 20 l/day
Share of leaking toilets with flush valves rather than siphons: 81 %

Leaky Loo Position Statement

Waterwise · untraceable source

Single leaking toilet: 215 to 400 l/day
Share of toilets leaking: 5 to 8 %
UK total from leaking toilets: 400000000 l/day

Methods for Calculation of Evaporation from Swimming Pools and Other Water Surfaces

M. M. Shah, ASHRAE Transactions SE-14-001 · primary source

Outdoor unoccupied pool evaporation: E0 = (C1 + C2 * u) * (pw - pa) / ifg kg/(m2*h)
C1, SI: 235 constant
C2, SI: 206 constant

Location-specific long-term averages, Wisley, Surrey

Met Office · primary source

Annual mean daily maximum temperature: 15.41 degrees C
Annual mean daily minimum temperature: 6.66 degrees C
Annual rainfall: 667.92 mm
Annual mean wind speed at 10 m: 5.06 knots

Annual bill

Discover Water, the water industry transparency site run with Water UK, Ofwat, CCW, the Drinking Water Inspectorate and Defra · primary source

Average annual household bill, combined water and sewerage: 639 GBP
Average annual household bill, water only: 309 GBP
Average annual household bill, sewerage only: 330 GBP

SI Brochure: The International System of Units (SI), 9th edition (2019), version 4.01, June 2026

Bureau International des Poids et Mesures · primary-standard source

cubic metre: coherent derived unit of the SI, Table 5 m3
litre: non-SI unit, Table 8. 1 l = 1 L = 1 dm3 = 10^-3 m3 l or L
bar: non-SI unit, Table 8. 1 bar = 0.1 MPa = 10^5 Pa bar

Authority URLs for the named entities in content/entities.ts

Various, see per-entity notes · primary source

WC flush volume: three UK instruments, not one

UK Statutory Instruments, Northern Ireland Statutory Rules, and Scottish Water · primary-standard source

Maximum single flush, all three jurisdictions: 6 litres
Dual flush, lesser flush maximum: two-thirds of the largest flush volume ratio
England and Wales transitional maximum, 1 Jul 1999 to 1 Jan 2001: 7.5 litres

Per-event central heating top-up volume, derived

Derived by Q3 from Boyle's law and typical UK domestic expansion vessel specifications · derived source

Water held in an expansion vessel: V_water = V * (1 - P0 / P), pressures absolute equation
Typical top-up, 8 l vessel at 1.0 bar pre-charge, 0.5 to 1.5 bar: 1.6 litres
Typical top-up, 8 l vessel at 0.75 bar pre-charge, 0.5 to 1.5 bar: 2.4 litres
Typical top-up, 12 l vessel at 1.0 bar pre-charge, 0.8 to 1.5 bar: 2.4 litres
Typical top-up, 8 l vessel at 1.0 bar pre-charge, 1.2 to 1.5 bar: 0.9 litres
Realistic range: 0.9 to 2.5 litres

Monodispersed Bubble Generation Using Hydrophobic Orifices: The Extended Tate’s Law

Bo Liu, Hao Zhang and co-authors, ACS Omega 2024, 9(17), 18854 to 18861 · primary source

This page publishes no figure for detection range, accuracy or the frequencies involved, and that is deliberate. No sourced measurement of any of them was found with a method behind it, and quoting one on a site funded by a company that sells this service would be exactly the kind of unchecked number this site exists to avoid.

Everything above is mechanism. Escaping water under pressure makes noise; sound travels along a pipe wall and through the ground; a stiffer pipe carries it further; two sensors and a time difference give a position. None of that is a claim about how often the method works, so none of it needs a success rate to stand up.

What is not claimed here: that acoustic detection usually works, or usually does not. Neither statement was sourceable. What is claimed is what it depends on, which is the part that lets you judge your own case.

What to do next

Three checks, and each one changes how a survey would go.

Look at the pipe at your internal stop tap and note whether it is plastic or metal. That single fact does more to predict how straightforward an acoustic survey will be than anything else you can observe.
Take your measured rate of loss with you. A very low rate is a harder acoustic job and it is better to say so at the start than to discover it on the day.
Note the noise around the property at the time of day a survey would run, and mention a main road, a pump or a neighbouring site when you arrange it.

What acoustic detection leaves unknown, even when it works, is depth and exact position: it narrows the search to a length of pipe rather than marking an X. What it cannot tell you at all is whether there is a second leak further along, because it finds the loudest point and stops.

Common questions

How does listening find the position?: The sound is loudest at the leak and falls away in both directions, so a listener comparing several points along the run can work out where the peak is. On a longer buried run two sensors are used at once, and the position is worked out from the tiny difference in when the same sound reaches each of them.
Why does plastic pipe make it harder?: Because the sound has to travel through the pipe wall to be heard from anywhere except directly above the leak, and a rigid pipe carries it further than a flexible one. A plastic supply pipe damps the noise over a shorter distance, so there are fewer places it can be heard from, and the listening has to be done closer to the leak that nobody has located yet.
Will it work if my leak is very small?: It may not. The noise comes from water being forced through a small opening, so a very slow loss makes very little of it. That is the awkward case: the leak is real, the meter has measured it, and there may not be enough sound to find it by listening.
Does noise around the house matter?: Yes, and more than people expect. Traffic, a pump, a fridge, rain on the ground and wind all sit in the same range as the sounds being listened for. It is why surveys are often done at night, and why it is worth mentioning a noisy road or a neighbouring site when you book rather than on the day.
Can I do this myself with a stethoscope or a phone app?: Not usefully. The problem is not amplification, it is separating one faint continuous sound from everything else at the same pitch, which is what the equipment and the operator are actually for. You are better off spending the effort on the stop tap test, which costs nothing and narrows the area more than an untrained listen will.