It depends which side of the boundary stop tap the leak is on. The water company owns and maintains the water main and the "communication pipe" that runs from the main to your property boundary, usually marked by an external stop tap or meter box. From that point into your house, the "supply pipe" belongs to you, even where it crosses your own garden or driveway. If the leak is confirmed on the water company's side, they'll repair it at no cost to you. If it's on your side, the repair cost is yours, though some water companies operate assistance schemes and rebates worth checking before you arrange your own repair.
Understanding the Pipe Network: Where the Boundary Sits
Every property connected to the mains water network has two distinct sections of pipe serving it, and the terminology matters because it's what water companies use to determine who pays for a repair. The Water Industry Act 1991 draws the same distinction: a "communication pipe" is the section a water undertaker is required to lay and maintain up to the boundary, while a "supply pipe" is everything beyond that, which the undertaker has no obligation to lay or maintain.
In practice, this is marked on the ground by the external or boundary stop tap, often a small metal cover set into the pavement or at the edge of a front garden. That single point is usually the cleanest way to work out which side a leak falls on.
Water Main & Communication Pipe
The pipe under the street and the branch that runs from it to your property boundary. Owned, laid and maintained by the water company.
Water CompanyPrivate Supply Pipe
The pipe running from your boundary stop tap into your house, including any section that crosses your garden or driveway. This is your responsibility.
HomeownerShared Supply Pipe
Some properties, particularly older terraces, share a single supply pipe from the main. Responsibility and repair costs are typically split between the properties served.
SharedWhat to Do If You Suspect an External Leak
Before assuming which side of the boundary a leak sits on, or arranging a costly repair, a few simple checks can save you money and wasted time.
Locate Your Boundary Stop Tap
This is usually a small metal or plastic cover set into the pavement, front garden or driveway, close to the edge of your property. It marks the transfer point between the water company's pipe and yours.
Check Your Water Meter
Turn off every tap and appliance in the property, then check whether the meter is still moving. If it is, water is escaping somewhere on your side of the meter.
Contact Your Water Company Before Assuming Cost
Report any suspected external leak to your water company first. If it's on their pipework, they'll investigate and repair it at no cost to you, and they can often help confirm which side of the boundary the fault is on.
Get a Specialist Investigation If It's Your Pipe
Once confirmed as a private supply pipe leak, a specialist using acoustic or tracer gas detection can pinpoint the exact fault location, avoiding unnecessary excavation across your garden or driveway.
Pipe Sections & Who's Responsible
Working from the street towards your house, here's how responsibility is typically divided across each section of pipe.
Water Main
The large pipe running under the street that supplies water to multiple properties in the area.
Water CompanyCommunication Pipe
The branch pipe connecting the water main to your property boundary, laid and owned by the water company.
Water CompanyBoundary Stop Tap & Meter
The valve and meter marking the transfer point, usually at or near the property boundary. Ownership and maintenance normally sit with the water company.
Water CompanySupply Pipe
The pipe running from the boundary stop tap into your house, including any section beneath your garden or driveway.
HomeownerInternal Plumbing
Everything past your internal stop tap, including all pipework, taps and appliances inside the property.
HomeownerConfirmed it's your side of the boundary? Tell us what you've found and we'll match you with a specialist and a fixed-price quote.
Get a Fixed-Price QuoteWater Company Assistance Schemes
Before arranging and paying for your own repair, it's always worth checking what your water company can offer. Policies vary between suppliers and change over time, so treat the following as a starting point for that conversation rather than a guarantee.
What to Ask Your Water Company
- Free repair or assistance schemes. Several UK water companies operate schemes offering a free or subsidised repair for a supply pipe leak, particularly for a customer's first reported leak.
- Thames Water's supply pipe offer. For customers across most of London, Thames Water has previously offered to repair supply pipes up to a set length and diameter at no cost, subject to circumstances, so it's always worth asking directly.
- Wasted water rebates. Metered customers who have repaired a confirmed supply pipe leak can often claim back the cost of the water that was lost, typically within a set window after the repair.
- Financial hardship and priority services support. Customers registered for financial support or a priority services register may be eligible for additional help with leak repair costs.
- Always confirm current terms. Assistance schemes, eligibility criteria and rebate windows change, so check directly with your supplier before assuming what is or isn't covered.
Responsibility by Scenario
The table below sets out how responsibility typically falls across common external leak scenarios.
| Scenario | Likely Responsibility | Notes |
|---|---|---|
| Leak in the water main under the road | Water Company | Report directly; repaired at no cost to residents |
| Leak in the communication pipe (main to boundary) | Water Company | Their pipe, their obligation to maintain and repair |
| Leak in your private supply pipe (boundary to house) | Homeowner | Worth checking for an assistance scheme or rebate first |
| Leak in a supply pipe shared with neighbours | Shared | Cost typically split between the properties served |
| Supply pipe leak under a neighbour's land or the road | Homeowner | Still your pipe even where it crosses land you don't own |
| Leak or fault in the water meter itself | Water Company | The meter is normally owned and maintained by the supplier |
| Leak past your internal stop tap, inside the property | Homeowner | Covered by home insurance rather than the water company |
Common Mistakes When Dealing With an External Leak
A handful of avoidable mistakes account for most of the confusion and unnecessary cost around external leaks.
Assuming It's the Water Company's Problem
Many homeowners assume any leak found underground in a garden or driveway must be the water company's responsibility. In practice, the section from the boundary stop tap into the house belongs to the homeowner in the vast majority of cases, even where it's several metres from the house itself.
Not Doing the Meter Test First
A simple meter check, turning off every tap and appliance and watching whether the meter keeps moving, costs nothing and quickly establishes whether the leak is even on the private side of the boundary before anyone needs to be called out.
Repairing Without Confirming Ownership First
Digging up a pipe that turns out to be shared with a neighbour, or that actually belongs to the water company, can create disputes over who should have paid. Confirming ownership first, either through your water company or a specialist investigation, avoids this entirely.
Detection & Repair Cost for External Leaks
Once you've established the leak is on your side of the boundary, here's what detection and repair typically cost.
| Cost Type | What's Typically Included | Typical Range |
|---|---|---|
| Specialist detection (underground supply pipe) | Acoustic or tracer gas survey, engineer time, written report | £600 - £1,200 |
| Excavation & repair of the private supply pipe | Digging, pipe repair or replacement, reinstatement | £220 - £440 average |
| Full trace and access | Detection plus the access work to reach the confirmed fault | £950 - £1,500+ |
| Repair on the water company's side of the boundary | Investigation and repair of the communication pipe or main | No cost to the homeowner |
For a fuller breakdown of what drives detection pricing up or down across leak types, see our water leak detection cost guide. If your buildings insurance includes Trace and Access cover, the cost of locating a private supply pipe leak may be partially or fully recoverable, so it's worth checking your policy before booking.
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