Underground Water Leak Detection

A buried leak is easy to miss and expensive to ignore. The pipe that carries water from the boundary of your property to your house runs underground, out of sight, and when it fails the water often drains away into the soil rather than showing indoors. The first warning most people get is a water bill that has jumped for no obvious reason.

DCI Leak Detection has spent more than 30 years finding hidden leaks across Cornwall and Devon. We locate underground leaks with specialist equipment first, so any digging that follows is one small, targeted hole rather than a trench across your lawn.

🕳️ How to tell the leak is underground

Underground leaks rarely announce themselves. Watch for these signs:

If the meter test points to a leak, our guide on how to find a water leak underground explains what you can check yourself before calling us. And if the wet ground sits between your water meter and the house, the problem is almost always the buried supply pipe. We cover that exact scenario in our article on a water leak between the meter and the house.

🎧 How we find buried leaks without digging

Supply pipes in the UK must be buried at least 750mm deep, and no deeper than 1350mm, under the Water Fittings Regulations. At that depth you cannot see, hear or feel a leak from the surface without the right equipment. Guesswork means holes, and holes cost money.

We start by tracing the pipe route with electronic locators, so we know exactly where the pipe runs before we test it. If you want the background, read our guide on how to locate water pipes underground. Then we apply the detection method that suits the pipe, the ground and the leak:

Acoustic correlation

Sensors placed at two points on the pipe record the noise the leak makes. The correlator compares how long the sound takes to reach each sensor and calculates the leak position between them. It is the standard method for pressurised supply pipes, and part of our wider acoustic leak detection service.

Ground microphones

Highly sensitive listening equipment amplifies the sound of escaping water through soil, concrete and tarmac, letting us narrow the leak down to a precise spot on the surface.

Tracer gas

We drain the pipe and fill it with a mix of 5% hydrogen in 95% nitrogen, which is classed as non-flammable and completely safe. The gas escapes at the leak, rises through the ground, and our surface detectors pick it up. It finds leaks that make no usable noise. More on our tracer gas leak detection page.

Thermal imaging

Where a buried leak changes the ground temperature, for example a hot water or heating pipe under a floor slab, our FLIR cameras show the pattern without touching the surface. See thermal imaging leak detection for how this works.

No single method works everywhere, which is why we carry all of them. Cornwall’s granite carries sound differently to Devon’s clay, and a quiet seep on a plastic pipe needs a different approach to a hissing crack in old copper. We combine methods until the result is confirmed, then mark the leak position on the surface.

📏 Who is responsible for an underground supply pipe?

This catches a lot of homeowners out. Ofwat and the Consumer Council for Water both set it out the same way:

• The water company owns the water main in the road and the communication pipe that runs from the main to the boundary of your property, usually up to the outside stop valve or meter.
• You, the property owner, are responsible for the supply pipe from that boundary point all the way into your home, including the section buried under your garden, path or drive.

So if the leak sits between the boundary and the house, finding and fixing it is your responsibility, not South West Water’s. Where one supply pipe serves several properties, responsibility for the shared section is normally shared between the owners. Our guide to who is responsible for a water leak walks through the boundary rules in plain English.

There is some good news. If a leak on your supply pipe has inflated a metered bill, South West Water runs a leak allowance scheme: repair the leak promptly and you can apply for an allowance towards the water that was lost, normally once per property. We explain how to claim in our guide to the South West Water leak allowance. For leaks on the mains side, or pressure problems traced back to the supply, our mains water leak detection service covers the full supply run.

🧱 Leaks under driveways, concrete and gardens

The thought of breaking up a block-paved drive or a concrete slab to chase a leak is what stops most people picking up the phone. It should not. The whole point of professional detection is that the surface only gets opened once, in the right place.

Because we trace the pipe route and confirm the leak position before any digging, the repair excavation is typically a single small hole over the marked spot. Under a lawn that means one neat turf cut. Under a drive or path it means lifting a small area of paving rather than the lot. Where a pipe has failed badly and needs replacing, we can advise on moling, a trenchless technique that pulls a new pipe through the ground between two small pits instead of digging a trench.

Leaks under floor slabs inside the house respond to the same approach: thermal imaging and acoustics narrow the area, so any opening of the floor is kept to a minimum.

🛡️ Insurance and trace and access

Most buildings insurance policies include trace and access cover. In plain terms, it pays the cost of finding the source of a water leak and making good the damage caused by getting to it, for example reinstating the section of drive or floor that had to be opened. The repair of the failed pipe itself is often not covered, and cover limits and terms vary between insurers, so check your policy before you claim. Our plain-English guide to what trace and access cover is explains the details.

Every DCI underground leak survey comes with a written report: where the leak is, how we confirmed it, photographs and our findings. These reports are produced for insurance use and give your insurer the evidence a trace and access claim needs. If you would rather hand the whole job over, our trace and access plumbers page covers the full service.

📋 What to expect when you book DCI

And the promise that matters: on residential jobs, if we do not find the leak, you do not pay. No Find, No Fee, subject to terms.