Thames Water Leak Detection London
Thames Water is responsible up to your boundary stop tap. Everything beyond it — the supply pipe under your garden, driveway and floor — is yours. We locate private-side supply pipe leaks across London with acoustic cross-correlation and repair them within your 4-week Section 75 window.
No find, no fee on all acoustic surveys. Same-day response across Zones 1–3. Detection from £280. We provide the documentation for your Thames Water leak allowance claim.
Landline 0207 046 1363 • WhatsApp 07456 975436 • Co. No. 17120057
If Thames Water has notified you of a leak, you have 4 weeks to fix it. Supply pipe detection costs £280–£420 with a no-find no-fee guarantee. Mole-and-replace under driveways costs £680–£1,200. We provide all the documentation to claim your Thames Water leak allowance within 3 months of the repair.
Thames Water private pipe leaks — where the responsibility boundary sits
Thames Water manages one of the largest water distribution networks in the world, supplying 15 million people across London and the Thames Valley. When a leak occurs somewhere on that network, the question of who pays to fix it turns on a precise legal and physical boundary that most homeowners have never had reason to think about — until the letter arrives.
Every property in the Thames Water area has a boundary stop tap, also called an external stop tap or communication stop, usually located in a small box in the footpath or pavement at the edge of the property. That boundary box is the exact demarcation point between Thames Water's infrastructure and the homeowner's. Thames Water is responsible for everything from the water main under the road up to and including that boundary box. The homeowner is responsible for everything downstream: the supply pipe running from the boundary box through the garden or driveway, under the floor and to the internal stop tap inside the house — and all plumbing beyond it.
Thames Water's own published pipe responsibility guidance confirms this. When their flow monitoring detects an unusual overnight consumption pattern on your meter, they notify you by letter rather than repair it themselves — because the leak is on your pipe, not theirs. That letter starts a 4-week clock under Section 75 of the Water Industry Act 1991, and what you do in those 4 weeks determines whether you pay once or twice.
Who is responsible for what — the exact boundary
Thames Water is responsible for:
- The water main under the road
- The communication pipe from the main to your property boundary
- The boundary stop tap / boundary box itself
- Their own metering equipment
You are responsible for:
- The supply pipe from the boundary stop tap into your property
- The section under your garden and driveway
- The section under your floor to the internal stop tap
- All internal plumbing throughout the property
The boundary stop tap is the exact demarcation point. If the leak is on Thames Water's side of it, they fix it for free. If it is on your side — which it almost always is when they write to you — you fix it. The letter they send confirms this: it refers you to a private plumber, not to their own repair teams.
What happens when Thames Water contacts you about a leak
Thames Water monitors overnight flow rates on smart meters across their network. An unusual constant flow overnight — when no taps or appliances should be running — is a reliable indicator of a leak. When they detect one on your meter, the process runs as follows.
Thames Water detects unusual flow
Their smart meter records a constant consumption overnight — typically 4–20 litres per hour with all taps and appliances off. This indicates a leak somewhere between the meter and your internal stop tap.
They notify you by letter
A letter arrives informing you that a potential leak has been detected, confirming the leak is on your private supply pipe, and directing you to arrange a repair. This letter date starts the 4-week clock under Section 75 of the Water Industry Act 1991.
You have 4 weeks to repair it
4 weeks from the letter date. Not from when you call a plumber, not from when you book a survey — from the letter date. Same-day detection is available across Zones 1–3, and most supply pipe repairs can be completed within 2–5 working days of detection.
If you don't fix it, Thames Water fixes it and charges you
If the 4-week window passes without a confirmed repair, Thames Water is entitled under Section 75 to arrange the repair themselves and invoice you for the work at their own contractor rates — which are significantly higher than private contractor rates. You also lose the right to claim the leak allowance.
If you fix it on a metered property, claim the leak allowance
Once the repair is complete, you can claim a Thames Water leak allowance — a rebate for the water lost while the leak was running. The claim must be submitted within 3 months of the repair date. We provide all the documentation Thames Water requires to process it: plumber's invoice, repair description, before and after meter readings.
Services we provide for Thames Water private pipe leaks
Every service below is available same-day across Zones 1–3. We handle the entire process from detection through repair to lease allowance claim documentation.
1. Supply pipe leak detection — no find, no fee
Acoustic cross-correlation and ground microphone survey of the MDPE supply run from your boundary stop tap to your internal stop tap. Locates the leak to within 25–40 cm under driveways, gardens and floors without excavation. If we cannot locate the leak, you pay nothing for the survey.
2. Supply pipe repair — patch or mole-and-replace
Once located, we repair the leak with the least-disruptive method available. Patch repair for accessible or soft-ground runs. Directional mole boring under block paving, concrete or tarmac driveways — single access point at each end, no full excavation. Full supply pipe replacement where the existing pipe is corroded or undersized.
3. Internal plumbing leak detection
If Thames Water's letter identifies an overnight flow but our initial pressure test at the boundary stop tap shows no loss — the leak is internal. We escalate to a full acoustic correlator survey of the internal pressurised system: cold mains, hot water and heating circuits.
4. Thames Water leak allowance claim support
We produce the plumber's invoice, repair description, pipe material confirmation and access photographs that Thames Water requires to process a leak allowance claim. The claim form is submitted by you within 3 months of the repair date; we ensure the supporting pack is complete and correctly formatted before you send it.
5. Insurance trace and access report — ABI format
If your buildings insurance includes trace and access cover — and approximately 97% of UK standard policies do — our written report qualifies for the claim. It includes engineer qualifications, equipment details, pressure-test readings, correlator graphs, photographs and the repair recommendation. Formatted to the ABI domestic trace and access protocol. Add-on cost of £100.
How we detect a supply pipe leak — step by step
Every supply pipe detection visit follows the same four-step procedure. Total on-site time for a standard domestic supply pipe survey is 75–120 minutes. Detection and a patch repair can usually be completed on the same visit.
Pressure test at boundary stop
20 minEngineer isolates the supply at the boundary stop tap and fits a calibrated gauge to the internal stop. A pressure drop over 20 minutes confirms a leak between the boundary and the house — essential before any scanning begins and the fastest way to rule out an internal plumbing fault.
Acoustic ground microphone scan
30–45 minA Sewerin AquaTest T10 or Vivax HL-7000 ground microphone is walked along the suspected pipe run. The hiss of escaping water from the MDPE supply is filtered through a 100 Hz–4 kHz band-pass and amplified across the driveway, garden or footpath surface to identify the loudest point above the pipe.
Cross-correlation pinpoint
20–40 minTwo contact sensors clamp to the boundary stop tap and to the internal stop tap. The SeCorr 08 / Correlux P200 computes the time-of-arrival difference of the leak noise and triangulates the leak position to within 25–40 cm — even through 100 mm of concrete or tarmac. One targeted access point, not a trench.
Mark, quote repair, claim leak allowance
15 minLeak is marked on the surface. A fixed repair quote is confirmed on the day — patch repair or mole-and-replace depending on driveway construction. We also provide the Thames Water documentation needed to claim your leak allowance within 3 months of the repair date.
Thames Water supply pipe leak — 2026 pricing
All prices below are fixed by job type and confirmed on the call based on your property, driveway type and access. No VAT add-ons, no parking surcharge, no out-of-hours premium on scheduled work. Same-day emergency call-outs are the only premium rate.
| Service | Scope | Typical Cost |
|---|---|---|
| Supply pipe detection survey | MDPE supply from boundary stop to internal stop, acoustic + ground microphone. | £280–£420 |
| Emergency supply pipe detection | Same-day, Zones 1–3, within 60–120 min. | £380–£550 |
| Supply pipe repair — patch | Open repair on located section, copper/MDPE fitting. | £380–£580 |
| Mole-and-replace under driveway | Directional mole boring under block paving/concrete. | £680–£1,200 |
| Full supply pipe replacement | New MDPE run from boundary to internal stop, including excavation. | £1,200–£2,800 |
| Insurance trace & access report | ABI-format written report for insurance claim submission. | +£100 |
* Prices include VAT. Full pricing list on the pricing page. Insurance trace and access cover usually pays for detection and access repair.
Why customers choose ERL for Thames Water private pipe leaks
- No Find No Fee — if we cannot locate the leak on the survey, you pay nothing for it.
- Work with your insurer — trace and access cover on most buildings policies pays in full.
- Thames Water leak allowance documentation — we produce everything TW needs to process your rebate.
- Act within your 4-week Section 75 window — fix it before Thames Water does it at their own rates.
- Same-day emergency response across Zones 1–3 — on site in 60–120 minutes.
- Mole-and-replace under driveways — single access point, no excavating across the whole drive.
Areas covered
Supply pipe leak detection and repair is attended across every London borough in the Thames Water supply area. Heaviest booking volumes come from Camden, Islington, Hackney, Ealing, Wandsworth and Lewisham where Victorian-era terrace stock carries ageing lead and iron supply pipes that are most likely to spring a pinhole leak.
Frequently asked questions
Is my leak Thames Water's responsibility?
Thames Water sent me a letter about a leak — what do I do?
What is the Thames Water leak allowance?
How do you find a leak under a driveway without digging it all up?
What does 'no find, no fee' mean?
Will my buildings insurance cover this?
How much does it cost to fix a supply pipe leak under a driveway?
How long does the 4-week Thames Water deadline run from?
Act within your 4-week Thames Water window
Same-day detection available across Zones 1–3. No find, no fee on all acoustic surveys. Detection from £280, mole-and-replace from £680. We provide the Thames Water leak allowance documentation.
No find, no fee • £5M PL insured • WRAS approved • Thames Water registered • Co. No. 17120057
Service area
Service Area — All London Boroughs
Thames Water supply pipe detection and repair is attended across all 32 London boroughs plus the City of London. Same-day attendance in Zones 1–3 within 60–120 minutes. Zones 3–6 within 2–4 hours.
Call before your 4-week window closes
No find, no fee. Fixed detection price confirmed on the call. Same-day attendance available. Leak allowance documentation included.