Underground Supply Pipe Leaks: What the Law Says About Who Is Responsible

Who owns which part of the pipe?

The run of pipework between the water main and a kitchen tap is owned by at least two parties, and in a converted London terrace it can be four. Almost every dispute about an underground leak is really a dispute about which party owns the failed section, and that question has a statutory answer rather than a negotiable one.

Section 219 of the Water Industry Act 1991 defines a communication pipe as so much of a service pipe as the water undertaker could be, or could have been, required to lay under section 46 of the same Act. A supply pipe is defined simply as so much of a service pipe as is not a communication pipe. In plain terms the communication pipe runs from the main to the property boundary and belongs to the water company; the supply pipe runs from the boundary into the building and belongs to the property owner. Ofwat, the economic regulator, sets out the same division for household customers, and each company restates it in its own leakage code of practice.

Section of the chain	Who owns it	Who repairs it	Who pays for the water lost
Water main in the highway	Water company	Water company	Water company
Communication pipe, main to boundary	Water company	Water company	Water company
Boundary stop tap and, where fitted, the external meter	Water company	Water company, absent wilful damage	Water company
Supply pipe, boundary to the building	Property owner	Property owner	Owner, because the meter records it
Internal pipework and fittings	Property owner	Owner, or landlord in a let home	Owner
Shared supply pipe serving two or more properties	Jointly, all properties served	Jointly	Apportioned between them

A pipe that crosses someone else's land is still yours

Thames Water states the position bluntly: if your supply pipe crosses land belonging to someone else, you remain responsible for it up to the point where it connects to the communication pipe or the main. That matters in London, where shared driveways, rear gardens and converted side returns routinely put a private supply pipe under ground the owner does not control. The repair obligation does not move with the soil. What does change is access, which is worth resolving before an excavation is booked.

Where is the boundary stop tap, and why does it decide liability?

The boundary stop tap, also called the external stop valve or the company stop tap, is the physical marker of the legal line. It normally sits in a small chamber under a metal or plastic cover at or just outside the property boundary, often in the footway. It is not the same thing as the internal stopcock under the kitchen sink, and confusing the two is the most common reason a householder concludes the water company is responsible when it is not.

Locating it is the first step in any underground investigation, because it frames everything that follows. A leak on the highway side of that valve is the company's problem. The same leak two metres further in is yours.

• Look for a small square cover near the front boundary, often marked with a W or the word water.
• Check whether the cover holds a meter as well as a valve, which is common on newer connections.
• If nothing is visible, the water company holds a record of the connection point and will usually confirm it.
• Where the record is unclear, pipe tracing equipment follows the supply line from inside the building outwards, which is quicker than hunting for a buried chamber.

Older London connections do not always follow the tidy model. On some streets the stop tap sits well inside the highway; in converted properties a single valve often controls a supply that has since been split. Establish the physical layout before anyone states a legal conclusion, which is what an underground water leak detection survey is for.

What does the Water Industry Act 1991 say about a leaking supply pipe?

Ownership tells you who may repair the pipe. Statute tells you what happens if nobody does. The relevant provision is section 75 of the Water Industry Act 1991, which applies where a water undertaker has reason to believe that water is being, or is likely to be, wasted, misused or unduly consumed, as well as in cases of contamination or damage.

Where that belief is held and the case is not an emergency, the undertaker may serve a notice on the consumer requiring specified steps to be taken. The Act requires the period given for compliance to be not less than the period of seven days beginning with the day after the notice is served. If the steps are not taken within that period, the undertaker may take them itself and recover its expenses from the person on whom the notice was served. There is a limit on that power: where the steps turn out to have been unnecessary in the circumstances, the undertaker cannot recover its costs and must meet the expenses of others who incurred them.

What a section 75 notice means in practice

The notice sits at the end of a sequence rather than the start of one. Thames Water's leakage code of practice states that where a leak has not been fixed within six weeks it may send a legal notice under section 75 explaining that it will fix the leak in accordance with its statutory duties, and that it may look to recover reasonable costs. It also reserves the right, in an emergency or where a leak may be causing damage, to turn off the supply until the repair is done.

Stage	What happens	Source of the rule
Leak identified	Either the company notifies the customer or the customer reports it	Company leakage code of practice
Repair window for the allowance	Thames Water household policy expects repair within four weeks of notification or identification	Thames Water leak allowance terms
Six weeks unrepaired	Company may serve a legal notice	Thames Water leakage code
Notice period	Not less than seven days beginning with the day after service	Water Industry Act 1991 s.75
Non-compliance	Undertaker may carry out the works and recover reasonable expenses	Water Industry Act 1991 s.75
Steps found unnecessary	No cost recovery; the undertaker meets others' expenses	Water Industry Act 1991 s.75

Alongside the Act sits the Water Supply (Water Fittings) Regulations 1999. Regulation 3(2) provides that no water fitting shall be installed, connected, arranged or used in such a manner that it causes or is likely to cause waste, misuse, undue consumption or contamination of water supplied by a water undertaker, or the erroneous measurement of that water. Regulation 3(3) applies the same prohibition to a fitting that, by reason of being damaged, worn or otherwise faulty, has that effect. A failed underground supply pipe is squarely within regulation 3(3), which is why leaving one to run is not merely expensive but a regulatory breach.

Who pays when a supply pipe is shared?

A shared supply is a single pipe serving two or more properties. Thames Water notes that this is more common where buildings sit close together in a side by side layout, which describes a large proportion of Victorian and Edwardian London housing stock. Where the supply is shared, the properties served hold joint responsibility for maintaining the shared section and for the associated costs.

Two consequences catch people out. A neighbour's refusal to contribute does not remove your own exposure, because the company deals with the properties served rather than one nominated owner. And there is no statutory formula for splitting the bill: apportionment is a matter between the owners, commonly in equal shares or by use, and the company will not arbitrate it.

How to find out whether your supply is shared

• Ask the water company for its record of the connection; shared supplies are usually flagged.
• Count the boundary chambers on the street. A terrace with one chamber serving three doors is a strong indicator.
• Close your internal stopcock and see whether a neighbour loses supply, which is the crudest and most conclusive test.
• Have the run traced physically, which also establishes the depth and route needed for any excavation.

This is not a formality. A repair paid for in full by one owner on a pipe that turns out to be shared is difficult to recover afterwards.

Can you get the water back on your bill?

A metered supply records everything that passes the meter, including everything lost to the leak. Leak allowances exist to put that right and are the part of this subject most often overlooked. Each company runs its own scheme under a regulator-approved code of practice, so conditions differ; what follows is Thames Water's published position, representative of the shape rather than the detail.

Thames Water requires the leak to be repaired within four weeks of it first notifying you or of the leak being identified, and the allowance to be claimed within three months of the repair date, even if no bill has yet arrived. Evidence is required in the form of a plumber's details and invoice, or a Thames Water job number if the company carried out the repair. The allowance is not available where section 75 has been used to force the repair. The credit is calculated by comparing meter readings from before, during and after the leak.

Point	Household supply, Thames Water published terms	Non-household supply, Thames Water code
Deadline to repair	Within four weeks of notification or identification	Within six weeks of the leak being confirmed
Deadline to claim	Within three months of the repair date	Within six months of the repair date
Who claims	The metered account holder	Through the customer's retailer
Frequency	Assessed on the claim	Normally once in twelve months
Period covered on customer-side pipework	Assessed from meter readings	Capped at a maximum of 365 days
What it pays for	The water lost, not the excavation or repair	The water lost, not the excavation or repair

Keep the invoice, dated photographs of the excavation and the meter readings either side of the repair, because claims fail on evidence far more often than on eligibility. Where a managing agent rather than the owner holds the metered account, agree who submits the claim before the repair is carried out rather than afterwards.

Will the water company repair or replace the pipe?

For households in the Thames Water area, generally no. Its published guidance directs customers to arrange their own repair and points those in financial difficulty towards its support schemes rather than promising a free fix. Other companies differ, and some run a first leak free repair scheme, usually restricted to external leaks and to the first occurrence. Check your own company's leakage code of practice before assuming either way.

Lead supply pipes and replacement

Lead is a separate question with a separate answer. The legal standard for lead in drinking water in England and Wales is 10 micrograms per litre under the Water Supply (Water Quality) Regulations 2016, enforced by the Drinking Water Inspectorate. Where a lead supply pipe is replaced, the usual industry pattern, and Thames Water's published scheme, is that the customer arranges and pays for replacement of the private supply pipe and the company then replaces the lead communication pipe on its side of the boundary at its own cost. Thames Water's eligibility conditions include a property built before 1970, suspected lead supply pipework, and a plan to replace the pipe within the next three months.

Because replacement is a full re-run rather than a patch, treat a lead pipe leak as a replacement decision from the outset. The excavation is the expensive part, and doing it twice is avoidable.

Does it change if the property is let or leasehold?

The ownership chain does not change, but who bears the cost within it can. In a rented home, section 11 of the Landlord and Tenant Act 1985 implies into most tenancies granted for a term of less than seven years an obligation on the landlord to keep in repair and proper working order the installations in the dwelling for the supply of water and for sanitation. A failed supply pipe serving the let dwelling sits inside that obligation, and it is the landlord's cost rather than the tenant's, unless the tenancy provides otherwise in a way the statute permits or the damage was caused by the tenant. The mechanics of notice and timescales are set out in our guide to landlord emergency repair responsibilities for tenanted homes.

In a leasehold building the supply pipe is usually part of the retained parts held by the freeholder, particularly where it serves more than one flat, but this is a question about the wording of the specific lease rather than a general rule. Where a single underground supply feeds a converted house in multiple occupation or a small block, the cost normally travels through the service charge, and the route for challenging it is the First-tier Tribunal rather than the county court. Disputes about liability between flats are a different problem again, covered in our guide for leaseholders and freeholders whose leak has damaged a neighbouring flat.

How the leak is located, and when to take advice

Locating the leak precisely turns a legal question into a manageable one, because it fixes the point of failure relative to the boundary and keeps the excavation small. On a pressurised supply, ground microphones and correlation are the usual first approach; under a driveway or slab where surface noise or pipe material defeats listening, tracer gas normally resolves it. Where each technique fails is set out in our guide to acoustic, thermal and tracer gas leak detection, and the options once the point is known are covered under water leak repair.

This article explains how the law allocates responsibility. It is not legal advice, and three situations genuinely need a solicitor rather than an engineer: a dispute with a neighbour about apportionment on a shared supply, a challenge to costs recovered by a water company after enforced works, and any question about an easement or right of access for a pipe crossing third party land. Where the dispute is with the water company itself rather than with a neighbour, the Consumer Council for Water will take up a complaint, and the Water Redress Scheme offers independent adjudication once the company's own complaints process has been exhausted.