Hidden pipework can be traced without drawings. Metal pipes are followed with an electromagnetic locator, plastic pipes with a sonde, acoustic tracing or tracer gas, and pipes inside walls and floors with thermal imaging. The route is marked on the surface first, because a leak can only be pinpointed on a pipe whose line is known.
Every older house in Cornwall has a version of this story. The farmhouse near Launceston has been extended three times since the war. The cottage in Helston had its kitchen moved to the other end in the seventies. The supply comes in somewhere near the old dairy, or possibly the lane, and the only person who knew for certain died in 1994. Now the meter is turning with everything off, or a wall is damp, and the first question is not “where is the leak” but “where on earth are the pipes”.
That is a fair question, and the answer is that pipework can be traced, on the surface and inside the building, without drawings and without opening anything up. Tracing is the first stage of most surveys we do on older properties, and it is the stage that decides whether the rest of the job takes an hour or a day.
Why so many Cornish homes have no pipe records
Granite and cob houses were built long before anyone plumbed them. Water arrived later, often from a well, a spring or a shared private supply before the mains reached the village, and each generation added pipe wherever it was easiest at the time. Copper laid in a screed over an earth floor. Galvanised steel run along a field hedge to a trough. Black alkathene pushed under a yard in the sixties. Blue MDPE for the extension in 2005, joined to whatever was already there.
None of this was drawn, and where it was, the drawing went with the previous owner. Building control records rarely show pipe routes. Even South West Water only knows its own side: the main, the communication pipe and the meter up to the boundary stop valve. Everything from that point to your taps is private and undocumented. If you cannot even find the internal stopcock, our guide to finding the stopcock in an older house is the place to start.
Start with what you can see
Before any equipment comes out, a walk round the property gives the first fixed points. We look for:
- The meter or boundary stop valve. This is one end of the supply pipe, usually in the verge or the gateway.
- The internal stopcock. The other end. Where the pipe surfaces inside tells you which wall it came through.
- Outside taps, troughs and old standpipes. Each one is a branch off the main run and a clue to its line.
- Changes in pipe material. A joint from steel to plastic at the back door usually marks where an old run was extended.
- Old hot water cylinders, tanks and blanked-off pipes. Inside, these show where earlier plumbing lived before the house was reorganised.
Between the fixed points, pipes tend to take the shortest sensible route a plumber could dig at the time. That gives a first guess, and the equipment then confirms or corrects it.
How buried water pipes are traced
Metal pipes: electromagnetic locating
Copper, steel and lead all conduct electricity. A signal generator is clamped to an exposed part of the pipe, usually at the stopcock, and puts a small signal along it. A hand-held locator picks that signal up through the ground and follows it, so the pipe’s line can be marked with paint or flags along the lawn, the yard or the drive. Most locators also estimate depth, which matters later when the hole is dug. Where the pipe runs close to an electricity cable or a metal fence, the signal can bleed, so we cross-check the line from more than one point.
Plastic pipes: sonde, sound and gas
MDPE and alkathene carry no signal, so they are traced by other means. Where there is access into the pipe, a small transmitter called a sonde is pushed along the bore and followed from above. Where there is not, a vibration can be put onto the pipe at one end and followed with a ground microphone. And where a leak is already suspected, tracer gas does two jobs at once: it follows the pipe and shows the fault. Old private supplies from a spring or borehole are almost always plastic and almost never recorded, so this is a large part of what we do on farms and smallholdings.
Pipes inside walls and floors
Indoors, a thermal camera is the quickest way to see a pipe. Run the hot tap or the heating and the pipe warms the plaster or the screed above it, showing up as a line on the camera. Cold pipes show the other way, as a cool line, particularly on a warm day. A pipe and cable detector picks up metal pipe behind plasterboard, and a moisture meter maps where water has spread from any fault. On a cob wall, where damp can rise as well as leak, this mapping is what separates the two; our guide to rising damp or a leak in a Cornish cottage goes into that in more detail.
Why tracing comes before leak detection
People sometimes ask why we spend the first part of a visit walking about with a locator when the leak is the thing they want found. The reason is that every method of pinpointing a leak depends on knowing the pipe’s line.
- Acoustic correlation calculates the leak position from the pipe length and material between two sensors. Get the route wrong and the calculation is wrong.
- A ground microphone only finds a leak if you listen over the pipe. On a pipe that takes a dog-leg round an old wall footing, listening in a straight line misses it.
- Tracer gas has to be introduced into the right section, with the right bits isolated, or it fills the wrong pipe.
- The dig needs a depth. A pipe at 400 millimetres under a yard and one at 900 millimetres under a drive need very different holes.
Tracing first is what turns an all-day search into a marked line and a single point. It is also why a plumber with a spade and good intentions so often ends up with three holes and no leak.
Tracer gas: finding the pipe and the leak in one pass
On an unrecorded plastic supply, tracer gas leak detection is often the method that solves both problems. The pipe is drained and filled with a safe mix of hydrogen and nitrogen at low pressure. Hydrogen escapes at the leak, rises straight up through soil, tarmac or concrete, and a detector swept across the surface reads highest directly above the fault. Because we sweep along the suspected route, the sweep itself confirms where the pipe runs. The gas is inert, non-toxic and dissipates harmlessly, and the pipe is flushed and returned to service the same day.
What you get at the end
The practical output of a tracing survey is a marked route on the ground and a sketch plan you can keep, showing where the supply enters, where it branches, what it is made of and roughly how deep it is. If a leak was found, its position is on the same plan, with the readings and images that support it. Insurers like this because it shows exactly why the ground or floor was opened where it was, and the next plumber, builder or owner will thank you for it. Our guide to what happens at a leak detection survey walks through the visit itself.
We trace and locate pipework as part of leak detection across the whole of Cornwall, and unrecorded rural supplies are something we deal with most weeks.
Frequently asked questions
How do you locate water pipes underground without any plans?
Metal pipes are traced by clamping a signal generator to an exposed section and following the signal with a locator above ground. Plastic pipes are traced with a sonde pushed along the bore, an induced vibration followed by ground microphone, or tracer gas swept along the surface. The route is then marked with paint or flags.
Can you trace a plastic water pipe?
Yes, although plastic carries no electromagnetic signal, so different methods are used. A sonde can be pushed along the pipe where there is access, a vibration can be applied and followed from above, or tracer gas can be introduced and detected at the surface along the route. Most rural Cornish supplies are plastic and are traced this way.
Can you find pipes inside the walls of an old cottage?
Usually. A thermal camera shows a hot or cold pipe as a line through plaster or screed once water has run through it, a pipe and cable detector finds metal pipe behind plasterboard, and moisture mapping shows where water has spread. On cob and granite walls this also helps separate a leak from rising damp.
Does South West Water know where my supply pipe runs?
Only up to the boundary. South West Water is responsible for the main, the communication pipe and the meter to the boundary stop valve, and its records stop there. The private supply pipe from the boundary into the house is the homeowner’s, and its route is very rarely recorded anywhere.
Will tracing the pipes damage my garden or drive?
No. Tracing is done from the surface with a locator, a ground microphone or a gas detector, and the only mark left is spray paint or flags along the route. Nothing is excavated until a leak has been pinpointed, and then only one hole is dug at the marked spot.
Find the pipe, then the leak
If nobody knows where the pipes run in your house or across your land, we will trace the route, mark it and pinpoint the leak from the surface. You get a plan to keep and a report your insurer can work from.
