Underground Water Mains Leak Detection in Daventry

Symptoms

The property in NN11 is a large detached house across three floors plus a cellar, served by a metered water supply at the property boundary. The incoming mains pipe runs approximately 180 metres from that boundary meter — largely adjacent to the driveway — before entering the building through a boiler room, where an elbow joint sits roughly 1 to 1.5 metres below external ground level.

Beyond these two known points, the route of the mains pipe beneath the grounds was entirely unknown prior to the investigation.

Methods Used

Once gas was detected at the back kitchen wall, the internal plumbing in that area was inspected, revealing an incoming MDPE blue plastic watermain. A gravel path outside was excavated to expose the services entering the building at that point — two drainage pipes, an oil feed, and the blue water mains.

Further gas testing and targeted excavation confirmed the leak on the watermain directly beneath the building, immediately adjacent to the exterior wall. Water mains leak detection of this kind — involving a long, unmapped supply run with no intermediate access points — requires a combination of gas injection timing, acoustic testing, and systematic surface scanning before any excavation is committed to.

Investigation Process

1. 1
   Site survey and pipe route assessment

   On arrival, the two known pipe locations — the boundary meter and the boiler room entry point — were confirmed. A survey of the grounds identified probable pipe routes running alongside drainage channels toward the rear of the property.

2. 2
   Mains isolated and tracer gas injected

   The incoming water supply was interrupted and hydrogen tracer gas injected into the exterior mains at 6.0 bar. Transit time to the leak point was measured at 5 minutes and 20 seconds.

3. 3
   Perimeter and route scanning

   Gas tracing and acoustic testing were conducted around the full property perimeter and along candidate pipe runs for approximately one hour with no surface detection during the initial phase.

4. 4
   Gas traces detected at back kitchen wall

   Gas was detected on the outside of the back wall of the back kitchen, directing the investigation to that specific area of the building.

5. 5
   Internal plumbing inspected

   The plumbing within the back kitchen was examined, identifying an incoming MDPE blue plastic water mains pipe serving that part of the building.

6. 6
   Gravel path excavated to expose services

   The gravel path at the back of the building was excavated to expose the services entering at that point: two drainage pipes, an oil feed pipe, and the blue water mains.

7. 7
   Leak confirmed under the building

   Further gas testing and targeted excavation confirmed the leak on the 25 mm blue MDPE water mains pipe, directly beneath the building immediately adjacent to the exterior wall.

8. 8
   Pipe section replaced

   A new section of 25 mm MDPE pipe was passed through the concrete screed and reconnected to both the internal and external feeds, eliminating the leaking joint under the building.

Result & Outcome

The repair was carried out by passing a new section of MDPE pipe through the concrete screed and reconnecting it to both the internal feed and the external supply, removing the faulty joint under the building entirely. A water mains leak detection investigation across a 180-metre unmapped supply run of this nature depends on accurate gas transit measurement to direct where effort is concentrated — in this case preventing any unnecessary disturbance to the driveway or wider grounds. A leakage allowance application to the water company was recommended to account for the volume lost during the period the leak was active.