Underground leak detection on your water supply pipe
Underground leak detection pinpoints escaping water along the buried supply pipe, the length between the water company's part and the house that Welsh Water and Hafren Dyfrdwy leave to the owner. Cambrian Leak Detection carries out this work for homes across Wales.
Which part of the underground supply pipe is yours in Wales?
The part of the underground supply pipe that is yours in Wales normally runs from the boundary of the street where Welsh Water's main is laid, or from just after Hafren Dyfrdwy's external stop tap, all the way to the house; Welsh Water adds that its rule holds even where the pipe crosses a neighbour's land.
Dŵr Cymru Welsh Water supplies most of Wales, and Hafren Dyfrdwy serves customers in north-east and mid Wales, so two owners on either company's water can be responsible for different lengths of pipe.
Welsh Water's code makes it normally responsible for its mains, any stop tap set in the road or pavement, and the stretch from the main to the street boundary, which it calls the communication pipe. The owner has the private supply pipe beyond it, which runs into the home and ends at the internal stop tap, plus all the pipework and fittings indoors. Its booklet adds that this is the split in most cases, and isn't always so.
Hafren Dyfrdwy's part runs up to and including its controlling external stop tap, the tap that shuts off one property's supply, normally at the property boundary. If that stop tap sits inside the boundary, the company owns the pipe from the street up to it and the owner owns the rest to the home.
Hafren Dyfrdwy says it can be hard to tell whether a property on the edge of its region is inside it, and asks people there to get in touch; its supply area page is the place to check.
Sources: Welsh Water, Final Water Resources Management Plan 2024; Hafren Dyfrdwy, About us; Welsh Water, Water Leaks Code of Practice; Hafren Dyfrdwy, Water pipe responsibility; Welsh Water, Private leaks; Welsh Water, Private leaks on your property; Hafren Dyfrdwy, Repairing leaks leaflet; Hafren Dyfrdwy, Our supply area.
What shows that water is escaping underground?
Water escaping underground shows as lush or greener grass, damp patches or sunken paving in dry weather, a big drop in water pressure, a hissing noise near the internal stop tap and, where a meter is fitted, a bill that rises without more use.
- Welsh Water's signs
- Areas of lush vegetation, a big drop in water pressure, a hissing noise near the internal stop tap, damp patches on the ground and an unexplained change on the bill.
- Hafren Dyfrdwy's signs
- Wet patches, greener grass, sunken paving and changes in pressure.
- A letter from Welsh Water
- If Welsh Water suspects or finds a leak on a customer's supply pipe, it tells the customer; its systems may show a leak in an area, which it checks and confirms is on that pipe.
Welsh Water says that because supply pipes are underground, it won't always be obvious when something is wrong with them. An unmetered Welsh Water home pays a set annual charge, so a leak leaves its bill unchanged, though Welsh Water still expects the leak repaired.
A gauge on the boiler that keeps falling is a different fault in the sealed heating circuit, and a boiler that keeps losing pressure has its own page.
Sources: Welsh Water, Network Leakage; Hafren Dyfrdwy, Report a problem; Welsh Water, Water Leaks Code of Practice; Welsh Water, Private leaks on your property.
What does the meter show when the supply pipe leaks?
The meter shows a supply pipe leak as a dial that keeps moving while the internal stop tap is shut: Welsh Water's test is to turn off the stop tap, check the kitchen cold tap has stopped, read the external meter and read it again half an hour later.
Shut the stop tap indoors
Close the internal stop tap; it usually sits under the kitchen sink.
Check the cold tap has stopped
Make sure the kitchen cold tap has stopped running, so nothing indoors is drawing water.
Take the first reading
Read the external meter if it is safe to reach. A Welsh Water meter is normally in the ground at the front of the property, at the boundary or in the pavement, and in rural areas it may be some distance away.
Read it again after half an hour
With the stop tap still closed, read the meter again. A dial that has moved may mean water is leaking somewhere on the pipe between the meter and the stop tap.
If the meter is inside the home, Welsh Water asks the household to contact it, and it arranges a visit to say how it can help. If a leak is found on the supply pipe when a meter is first fitted, Welsh Water advises on the options and does not start metered charging until the pipe is repaired.
Hafren Dyfrdwy's own check is for pressure rather than loss: time how long the cold kitchen tap takes to fill a 1-litre jug, with everything else off, and expect around 7 seconds.
Sources: Welsh Water, Water Leaks Code of Practice; Welsh Water, About your water meter; Hafren Dyfrdwy, Report a problem.
Which methods find the leak under a drive, path or lawn?
The methods that find a leak under a drive, path or lawn are acoustic listening with a ground microphone, which hears water escaping from a pressurised pipe, and tracer gas, which rises through concrete, tarmac, block paving and grass to a detector at the surface.
| Method | How it works | Its limit |
|---|---|---|
| Acoustic listening | Acoustic listening relies on the noise water makes as it escapes under pressure from a pipe: a listening stick placed on the pipework, or a ground microphone set down above the pipe's route, brings that noise to the listener, and it is loudest nearest the leak. | A quiet leak, or a pipe with no pressure in it, gives nothing to hear; for those, Sewerin recommends tracer gas. |
| Tracer gas | For a tracer gas test the pipe is drained and closed off, then charged with forming gas, 95% nitrogen and 5% hydrogen; wherever the pipe is broken the gas finds a way out and climbs to the surface, where a detector passed over the floor or ground picks up the strongest trace. | The gas can take very different times to reach the surface, depending on what lies above the pipe. |
| Pressure testing | In a pressure test, a sealed-off system or section is brought up to a set pressure and left for a fixed time with an eye on the gauge; if the reading falls, there is normally a leak somewhere in that section. | Plastic pipe expands slightly when pressurised and any trapped air must be let out first, so a gauge that drops is not, on its own, proof of a leak. |
Before either search, a meter test or a pressure test confirms that the pipe is losing water. Sewerin and INFICON both say the hydrogen and nitrogen mix used for tracer gas will not burn, is not poisonous and does not corrode.
Cambrian Leak Detection uses these methods from the surface, along the pipe's route, and the home page sets out leak detection services in Wales for every kind of leak. A result is never promised: Welsh Water itself will not try to pinpoint a leak on a part of the pipe under the property, a wall, a shed, a garage or any other structure.
Sources: Welsh Water, Water Leaks Code of Practice; Northumbrian Water, Guidance note 3: Pressure testing of new water service pipework; Sewerin, Listening stick W50; Sewerin, VARIOTEC 460 Tracergas; INFICON, Hydrogen leak detectors; Sewerin, AQUAPHON A 200; Sewerin, Stethophon 04; INFICON, Find Hidden Water Leaks Fast; Wunda, Phase 3: Preparing and connecting the pipe to the manifold; Grant UK, Why would an UFH system lose pressure?; Financial Ombudsman Service, decision DRN-4125471; Ideal, Topping up the pressure on your Ideal boiler.
How far will Welsh Water or Hafren Dyfrdwy help with your supply pipe?
Welsh Water and Hafren Dyfrdwy both help with a leaking supply pipe within limits: Welsh Water will try to pinpoint a household leak if four conditions are met, offers a free repair where possible and runs a Leak Support Scheme for owner-occupiers, while Hafren Dyfrdwy can offer domestic customers it has written to about a leak a free repair, subject to conditions.
| What each company offers | Welsh Water | Hafren Dyfrdwy |
|---|---|---|
| Where your pipe starts | At the boundary of the street where its main is laid. | Just past its controlling external stop tap, normally at the property boundary. |
| Finding the leak | Will try its best to pinpoint a household leak on the external supply pipe if it can establish where the pipe runs, the leak is large enough for its equipment, and the leak is not under a building or other structure. | Its responsibility page sets out no pinpointing offer; ask the company directly. |
| Repair offer | Says it “will offer a free repair where possible”, which its code calls an offer it may make, subject to certain conditions. | Can offer domestic customers it has written to about a leak a free of charge repair, subject to conditions; leaks covered by household insurance are not included. |
| Who qualifies | The Leak Support Scheme is for customers who own the home they live in; landlords and businesses arrange the repair themselves and tell Welsh Water when it is done. | Domestic customers it has written to about a leak, and it may ask to see the insurance policy. |
| Time to repair | 30 calendar days from the date it notifies you of the leak, under its code of practice. | No deadline is stated on its current pages; check its water pipe responsibility page. |
| Reporting a public leak | Report it on Welsh Water's Report an issue page, online at any hour. | Tell it through its Report a problem page, after checking the latest updates for the area. |
Welsh Water says some insurance policies cover leaks on supply pipes and advises checking yours, which matters on Hafren Dyfrdwy's water too, since insured leaks fall outside its free repair scheme. The page on insurance that covers a supply pipe leak explains what a policy's trace and access part pays for.
Sources: Welsh Water, Private leaks; Hafren Dyfrdwy, Water pipe responsibility; Welsh Water, Water Leaks Code of Practice; Welsh Water, Private leaks on your property; Welsh Water, Network Leakage; Welsh Water, Report an issue; Hafren Dyfrdwy, Report a problem.
Will the water company take the lost water off a metered bill?
Yes, it can: Welsh Water may give an allowance for the water and sewerage charges lost through a leak on the external supply pipe if it is repaired within 30 calendar days of notice and Welsh Water is told within 6 months of the repair, and Hafren Dyfrdwy reviews claims and may cover some or all of the water lost.
Welsh Water bills a metered home on what the meter records, leaks included. Its code of practice lists every condition for an allowance:
- Who pays the bill
- The owner-occupier, landlord or tenant who pays it.
- Meter
- The home is metered.
- Where the leak was
- On the external supply pipe, not on internal fittings.
- Repair
- Within 30 calendar days of Welsh Water's notice, where it has no further help to offer.
- Telling Welsh Water
- Within 6 months of the repair.
- Cause
- Not caused by negligence.
- Legal team
- No referral to Welsh Water's legal team.
- Earlier allowances
- None at that property during the past 2 years.
For a household, Welsh Water's allowance covers both the water and the sewerage charges on the wasted water, is worked out from normal usage and reaches back no more than 12 months before the repair date. A customer outside the criteria can ask Welsh Water to consider their circumstances.
Hafren Dyfrdwy says that if a leak at home has affected the bill, it may be able to help once the leak is fixed, reviewing the claim to see whether it can cover some or all of the water lost, depending on how long it was leaking; its leakage allowance page has the details.
Sources: Welsh Water, Water Leaks Code of Practice; Hafren Dyfrdwy, Leakage allowance.
Whose job is a supply pipe that feeds several houses?
A supply pipe that feeds several houses is the joint job of every property it serves: Welsh Water says responsibility is shared across all of them and recommends a separate pipe for each, and Hafren Dyfrdwy says everyone downstream of a leak is responsible for getting it sorted.
Welsh Water calls this a shared supply. When it finds one, it talks the repair options through with the owners, and where a shared supply keeps leaking unrepaired, its legal team can serve a notice requiring the properties to install separate supply pipes within three months. For owner-occupiers on a joint supply, the Leak Support Scheme can include a contribution towards a new pipe of their own, with a free reconnection to Welsh Water's main.
BBC News reported on 20 July 2026 that residents of five houses in Pontycymer, in the Garw Valley, were told by Welsh Water that a leak on the pipe shared by their homes was theirs to repair; the company said it does not own or manage that pipe, and told the BBC it had offered a free connection to its main if each property connected on its own.
Indoors, every pipe past the internal stop tap is the owner's to repair, and the page on hidden leaks on water pipes inside the house covers how those are found.
Sources: Welsh Water, Private leaks on your property; Welsh Water, Private leaks; Welsh Water, Water Leaks Code of Practice; Hafren Dyfrdwy, Repairing leaks leaflet; BBC News, Pontycymer shared water pipe report.