To find a water leak underground, start with a water meter test (all taps off, check if it still moves), look for wet patches or unusually green grass in the garden, and check for a drop in water pressure indoors. If nothing's obvious, a specialist uses acoustic listening equipment, tracer gas, or leak correlation to pinpoint the exact spot without digging up the whole pipe run.
In This Guide
Signs you have an underground leak
Learning how to find a water leak underground usually starts with noticing something's wrong before you know exactly what. An underground leak doesn't announce itself the way a burst pipe under the sink does. Water escapes into soil, disperses, and the only clues are indirect.
Common signs include a patch of grass that's greener and grows faster than the rest of the lawn, a section of path or driveway that stays damp long after rain has stopped elsewhere, a hissing or trickling sound near the ground with no obvious source, or water pressure indoors that's dropped for no clear reason. Any of these on their own could be something else. Together, they're worth taking seriously.
Step 1: the water meter test
This is the cheapest, fastest check anyone can do before calling a specialist. Turn off every tap, appliance and outdoor tap in the property. Find your water meter and note the reading, or watch the leak indicator dial if it has one. Wait fifteen minutes without using any water at all, then check again.
Reading the result
If the reading has changed, or the leak indicator has spun, water is escaping somewhere in the system between the meter and your fittings. It doesn't tell you where, only that a leak exists. Our guide on checking your water meter for a leak covers this test step by step with more detail on meter types.
Most Scottish homes pay for water through council tax rather than a meter, so this test mainly applies where a meter exists, typically business premises, some newer developments, or properties on a private supply.
Step 2: check the garden and pressure
Walk the boundary of the property, paying attention to where the supply pipe likely runs between the street and the house. Look for soft, waterlogged ground away from downpipes and drains, or a patch that never seems to dry out even in a dry spell. In winter, watch for a section of ground that stays free of frost when everywhere else is white, since escaping water keeps the soil slightly warmer.
Indoors, a sudden or gradual drop in pressure at taps and showers, especially if it's happened alongside a rising water bill or a damp patch appearing near an external wall, points toward a supply-side leak rather than an internal plumbing fault.
Listening for the leak itself
Acoustic listening equipment picks up the specific sound water makes escaping a pressurised pipe under soil or concrete. An engineer works along the suspected pipe run with a ground microphone, comparing sound intensity at different points to narrow down where the noise is loudest.
Whose pipe is it anyway
Before anyone starts digging, it's worth knowing who's responsible. According to Citizens Advice Scotland, Scottish Water is responsible for the mains pipe up to the property boundary, and the property owner is responsible for the pipe from the boundary or stopcock into and through the home. If your leak sits on your side of that boundary, the repair (and often the detection work) falls to you.
Our article on the leak between the meter and your house goes into this boundary question in more depth, including what to do if you're not sure which side the fault is on.
Acoustic listening explained
Acoustic leak detection is usually the first professional method tried, because it's fast and non-invasive. Water escaping a pipe under pressure creates a distinct sound as it forces its way through a crack or failed joint. That sound travels along the pipe and through the surrounding ground or concrete.
An engineer uses sensitive ground microphones at intervals along the suspected pipe route, listening for where the sound is strongest. It works well on shallower pipe runs and where ground conditions transmit sound clearly. It's less reliable on very deep pipes, in noisy urban settings, or where multiple services run close together underground.
Tracer gas for pipes acoustics can't reach
Where acoustic listening doesn't give a clear result, tracer gas is the next method. A safe mix of 5% hydrogen and 95% nitrogen is introduced into the empty pipe. Because hydrogen is the lightest gas and rises quickly through soil, any gas escaping at the leak point reaches the surface directly above the fault. An engineer then walks the route with a sensitive gas detector, and the reading spikes right where the leak is.
This method works well on deeper pipes, under driveways and patios, and in situations where background noise makes acoustic listening unreliable. It's one of the more precise ways to confirm an exact dig point before anyone lifts a slab.
Why gas rises straight to the fault
Hydrogen's low density means it doesn't spread sideways through soil the way sound or moisture can. It moves upward, so the strongest reading on the surface sits almost directly above the leak, which is what makes this method so precise for confirming a dig point.
Correlation: narrowing it to a metre
Leak noise correlation is a step beyond basic acoustic listening. Two sensors are placed on the pipe at known points, one on either side of the suspected leak area, often at valves or hydrants. Both record the sound of the leak simultaneously, and the very slight time difference between when each sensor picks up the noise is used to calculate the exact distance to the leak along the pipe.
This is particularly useful on longer runs of underground pipe, such as the supply between a meter and a rural property, or a mains run feeding several buildings, where acoustic listening alone would mean walking a long stretch of ground metre by metre.
DIY checks vs calling a specialist
Worth doing yourself
- Water meter test with everything off
- Visual check of the garden for wet patches or unusual growth
- Noting pressure changes and when they started
Needs specialist equipment
- Pinpointing the exact leak location under soil or concrete
- Confirming a fault on a deep or long pipe run
- Producing an insurance-approved report for a claim
Digging blind on the strength of a hunch is expensive and often wrong. A underground water leak detection survey combines acoustic listening, tracer gas and correlation as needed, so any digging that follows is targeted at a confirmed spot rather than a guess. Where the fault sits on the supply side rather than inside the home, our water mains leak detection team can also confirm whether the issue is on your pipe or the mains itself.
Not sure exactly where your underground leak is?
We use acoustic listening, tracer gas and correlation to find the fault before anyone lifts a spade, saving unnecessary digging across your garden or driveway.
Frequently Asked Questions
Look for signs outdoors: a patch of unusually green or fast-growing grass, ground that stays damp when everywhere else has dried out, or a hissing sound near ground level. Combined with a positive water meter test, these point to a leak in the underground supply pipe.
You can confirm a leak exists using a water meter test and by checking for visible surface signs, but pinpointing the exact location under soil or concrete needs acoustic listening, tracer gas or correlation equipment that isn't available to most homeowners.
A safe mix of 5% hydrogen and 95% nitrogen is pushed into the empty pipe. The gas escapes at the leak point and rises through the soil to the surface, where a sensitive detector picks up the strongest reading almost directly above the fault.
It works well on shallower runs where sound transmits clearly through the ground, but accuracy drops on very deep pipes or in noisy areas. In those cases, tracer gas or leak noise correlation usually gives a more precise result.
Scottish Water is responsible for the mains pipe up to your property boundary. From the boundary or stopcock into the home, responsibility sits with the property owner, according to Citizens Advice Scotland. That includes both the pipe itself and finding the fault.
No. Non-invasive methods like acoustic listening, tracer gas and correlation are used specifically to avoid that, narrowing the fault to a small, confirmed area so any digging that follows is targeted rather than exploratory.
Most underground surveys are completed same-day, combining a meter check, acoustic listening and, where needed, tracer gas on-site to give you a confirmed location before the engineer leaves.
📍 Professional Leak Detection Across Scotland
Get your underground leak confirmed, not guessed at
Our engineers use non-invasive thermal, acoustic and tracer gas methods to find underground leaks across Scotland, with insurance-approved reports available where you need one.