Leak detection - run the meter test first

What is leak detection?

Leak detection locates a water leak you cannot see - under a slab, inside a wall, beneath a yard - without demolishing the building to find it. Professionals use acoustic listening, thermal imaging, pressure isolation and sometimes tracer gas to narrow a leak to a small area before anything is opened. Before you book any of that, run the meter test below: it costs nothing and tells you whether a hidden leak exists at all.

Signs you need leak detection

• A water bill that has risen with no change in household use
• The sound of running water when every fixture in the house is off
• A warm patch on the floor, particularly on a slab - close to diagnostic for a hot-water slab leak
• Damp, musty smell or mould reappearing in the same place after cleaning
• The water meter dial moving with every fixture closed
• Pressure that drops overnight with no fixture use
• Flooring that lifts, cups or stays cool/damp in one zone
• You already fixed a visible drip and the meter still moves

Seeing something not on this list? Browse plumbing problems by symptom →

How leak detection actually works

1. 1

   The meter test - do this yourself, before you pay anyone

   Turn off every fixture and water-using appliance, including ice makers and irrigation. Note the meter reading, or watch the low-flow indicator. Wait without using water and check again; any movement means water is leaving the system. That free test is the gate that decides whether detection is even the right booking.

   Watch forA silent toilet flapper. It is the most common cause of a mysteriously rising bill and makes no sound. Put food colouring in each cistern, wait without flushing, and see whether colour reaches the bowl.

2. 2

   Isolate the hot side from the cold side

   Closing the cold inlet valve on the water heater and repeating the meter test splits the problem in half. Knowing hot versus cold narrows equipment choice and repair scope before anyone drills a floor.

   Watch forNobody isolating anything before deploying equipment. The gear is only as good as the area you point it at.

3. 3

   Acoustic detection and thermal imaging

   Pressurised water escaping through a small opening makes a noise that carries through pipe and structure; ground microphones trace it to within a foot or two. Thermal imaging maps temperature anomalies that often line up with hot-line leaks under slabs or in walls.

   Watch forThermal images treated as proof on their own. Sunlight on a wall, a heating duct or a recessed light all produce warm patterns. The image should corroborate acoustic or pressure findings, not replace them.

4. 4

   Pressure testing and tracer gas, for the hard ones

   A section of pipework can be isolated and pressure-tested to prove whether it holds. Tracer gas is reserved for stubborn cases where cheaper methods fail - it is powerful and should not be the default first line on every ticket.

   Watch forTracer gas quoted first. Reaching for it before the cheaper methods inflates the bill without improving the answer.

5. 5

   The report - what you are actually buying

   The deliverable is a located leak: a marked position, a depth or wall cavity, an assessment of the pipe involved, and ideally photographs and thermal images. Detection and repair are frequently separate jobs and sometimes separate companies - which is fine when the report is portable.

   Watch forNo written location report. A verbal "it's about there" cannot be taken to a second repair quote or to an insurer. Ask what the report includes before booking.

What does leak detection cost?

A professional leak detection appointment is typically priced as a flat fee for the visit, with harder methods such as tracer gas costing more. Repairing the leak is quoted separately and is usually the larger number, especially under a slab. Run the free meter test first.

See the full leak detection cost guide - by material, size and region →

If the number is the problem, here are the ways people pay for it →