You do not dig to find a buried leak, you dig once you have found it. Confirm it with the meter and stopcock test, then the pipe route is traced and the leak is pinpointed with acoustic correlation and tracer gas from the surface. The result is one small excavation at the marked spot, not a trench along the drive.
The water meter out at the lane keeps turning, the bill has crept up, and somewhere between the boundary and your front door a pipe is losing water under tarmac, block paving or a lawn you have spent years on. The obvious worry is the digger. Nobody wants a trench cut through the drive on the off chance the leak is somewhere along it. The good news is that a buried leak is one of the problems modern detection handles best, and the digging comes last, not first.
Why Cornish supply pipes are so often long and buried
In a town terrace the supply pipe might be five metres long. On a converted barn outside Bodmin, a farmhouse on the Lizard or a bungalow set back from a lane near Wadebridge, it can be fifty metres or more, crossing a field gate, a parking area and a garden before it reaches the house. Many of these pipes were laid decades ago in whatever material was to hand: galvanised steel, black alkathene, lead on the oldest properties, and blue MDPE on anything renewed since the 1980s.
Long runs mean more joints, more chances of a stone bearing on the pipe, more tree roots and more ground movement. Cornwall’s clay and shillet subsoil holds water in winter and shrinks in a dry summer, which works old joints loose. And because the pipe is deep, a leak can run for months before anything shows on the surface.
Signs the leak is under the drive or path
- A patch that stays damp when everything else has dried. After rain, the drive dries from the edges and one area stays dark for days.
- Greener, faster-growing grass in a strip or a circle. The classic sign on a lawn or verge that a pipe is feeding it from below.
- Paving that has sunk, tilted or lifted. Escaping water washes out the sub-base and the surface follows it.
- Moss or algae in one spot on tarmac. Constant moisture from beneath keeps it growing where nothing else does.
- Water standing in the meter chamber after dry weather, or a faint hiss at the boundary stop valve.
- Lower pressure at the kitchen tap than you remember, particularly first thing in the morning.
None of these prove a leak by themselves. A high water table, a blocked land drain or a neighbour’s downpipe can produce the same wet patch. That is why the next step is the meter.
Prove it, and find out whose pipe it is
Turn off every tap and appliance, note the meter reading, and leave it for an hour. If it has moved, water is escaping. Now close the internal stopcock, usually under the kitchen sink, and check again. If the meter carries on turning with the house isolated, the leak is on the buried supply pipe between the meter and the stopcock. Our step-by-step guide to the overnight water meter leak test shows how to make the reading reliable.
Ownership matters here. South West Water looks after the communication pipe and the meter up to the boundary stop valve. From that point into the house, the supply pipe is yours, including the section under the drive. If you are not sure which side your leak sits on, read who pays for the pipe before and after the meter before you ring anyone.
| What you notice | Most likely cause | What to do |
|---|---|---|
| Meter turns with the stopcock closed | Leak on your buried supply pipe | Book an underground survey, tell your insurer |
| Meter stops with the stopcock closed | Leak inside the house | Internal survey, check the heating and cisterns |
| Meter does not move, drive still wet | Drain, groundwater or surface water | Check gullies and land drains first |
| Water in the meter box, meter still | Rain or a leak on the company side | Report it to South West Water |
How a buried leak is found without a trench
Once the leak is confirmed on your pipe, an underground leak detection survey follows the same order every time: trace the route, then listen, then confirm.
Tracing the route
You cannot pinpoint a leak on a pipe you cannot follow. Metal pipes are traced with a signal generator and locator that follow the pipe’s own line under the ground. Plastic pipe carries no signal, so we trace it by other means, such as a sonde pushed along the bore or by following the acoustic signal from one end to the other. Either way, the route is marked on the surface before the leak work starts, which alone saves a great deal of guesswork on a long Cornish run.
Acoustic correlation
Two sensors are clamped to the pipe at accessible points, typically the boundary stop valve and the internal stopcock. Water escaping under pressure creates a sound that travels along the pipe in both directions. The correlator measures the tiny difference in the time that sound takes to reach each sensor and, knowing the pipe length and material, calculates where along the run the leak sits. A ground microphone then narrows it further by listening directly over the marked line.
Tracer gas
Where the pipe is plastic or the leak is too quiet to hear, the supply is drained and filled with a safe hydrogen and nitrogen mix. The gas escapes at the leak, rises through the sub-base and the surface, and a detector finds it above the fault. It works through tarmac, block paving and concrete, and on a sound pipe it confirms in minutes that there is no leak on that section at all.
One hole, not a trench
With the leak marked on the surface, the excavation is a single hole at that point. Supply pipes are typically laid around 750 millimetres deep, and often a little deeper under a drive to protect them from traffic and frost, so the hole is deeper than it is wide. Block paving is lifted and relaid. Tarmac is cut square and patched. A lawn is turfed back. The pipe is repaired or a short section replaced, tested under pressure, and the hole backfilled.
On a very old pipe with more than one fault, we may suggest a different route: leave the old pipe in the ground and mole a new MDPE supply alongside, which pulls a new pipe through with only a launch pit and a reception pit. That decision is easier to make when you know exactly where the leak is and what the pipe is made of, which is what the survey tells you.
Who pays for a leak under the drive
The pipe is yours, so the repair is yours. Two things soften that. South West Water offers a leak allowance on a first supply-pipe leak, subject to its conditions, which can credit back some of the water lost once the repair is done; our guide to the South West Water leak allowance explains how to apply. And many buildings policies extend trace and access cover to underground pipes within your boundary, paying to find the leak and to reinstate the drive or path afterwards, though never the pipe repair itself. Check your wording, and log the claim before the survey so the report can be written for the insurer.
We provide leak detection anywhere in Cornwall, and long rural supply runs are a large part of what we do.
Frequently asked questions
How do you find a water leak underground without digging?
The pipe route is traced and marked, then acoustic correlation measures how long the sound of the leak takes to reach sensors at each end of the run and calculates its position. A ground microphone and tracer gas confirm the exact spot from the surface, so only that point is excavated.
Can you find a leak under tarmac or block paving?
Yes. Correlation works on the pipe itself, not the surface, and tracer gas rises through tarmac, paving and concrete to be detected above the leak. Once the position is marked, block paving is lifted and relaid, and tarmac is cut and patched in one small square rather than along the whole drive.
Is the pipe under my drive my responsibility or South West Water’s?
South West Water is responsible for the communication pipe and the meter up to the boundary stop valve. The supply pipe from there into the house is the homeowner’s, including the part under a drive or path. A shared supply serving several houses is normally the shared responsibility of the properties on it.
Should I dig at the wet patch myself?
No. Water travels along the pipe bedding and surfaces where the ground is weakest, so the wet patch is often metres from the leak. Supply pipes are deep and share the ground with gas, electricity and drains. Locate the leak first and dig once, at the marked point.
Will I get a leak allowance from South West Water?
South West Water offers a leak allowance on a first supply-pipe leak, subject to its conditions, once the leak has been repaired. Keep your meter readings before and after the repair and the invoice for the work, then apply. It reduces the bill for lost water but does not pay for the repair.
Mark the spot, dig once
If the meter keeps turning and the drive or path is the suspect, we will trace the pipe, pinpoint the leak from the surface and mark exactly where to dig. You get an insurance-ready report to support a trace and access claim.
