Underground Water Mains Leak Detection in Mottram St. Andrew

Symptoms

The property in SK9 is a detached house fitted with an unvented cylinder and multiple stop taps — one internal stop tap in the garage, one behind the cloakroom basin, and an external stop tap on the front driveway. A suspected leak on the incoming water mains had already been investigated on a prior visit, but that inspection returned no conclusive results, prompting a second visit to carry out a more thorough assessment.

The property's pipework layout added complexity to the investigation. The incoming mains ran beneath the hallway floor and it appeared likely that the two supply points were joined together under the concrete kitchen floor — a section of pipework that could not be directly accessed or visually inspected.

This made it impossible to pinpoint the fault through observation alone.

For a water mains leak detection job like this — where the pipe route runs through inaccessible voids and under concrete — pressure testing combined with tracer gas provides the most reliable path to a confirmed result. That approach was adopted for this visit.

Methods Used

The investigation began by removing the downstairs cloakroom basin to access the secondary stop tap located behind it, then using an endoscope camera to trace the route of the incoming mains beneath the hallway floor. A floorboard was lifted to expose the pipe, but the tee-in point could not be located, pointing toward a junction concealed under the concrete kitchen floor.

Pressure testing was then carried out on the cloakroom mains, which confirmed a continuing pressure loss matching the previous visit's findings.

Tracer gas was introduced into the system and the mains were emptied via the garage stop tap. A full tracer gas survey was conducted across the relevant ground area.

High gas readings were detected immediately beside the external meter, and acoustic testing was applied to the same location to corroborate the finding before any excavation took place. Tracer gas is a well-established tool in water mains leak detection precisely because it reaches the surface even through compacted ground, making it reliable when a leak is too deep or too small to produce audible signals alone.

Investigation Process

1. 1
   Cloakroom basin removed

   The downstairs cloakroom basin was removed to gain access to the secondary stop tap located behind it, which was needed to isolate and test the mains supply from that point.

2. 2
   Camera survey of mains route

   An endoscope camera was used to trace the incoming mains beneath the property. The pipe was found running from the hallway and a floorboard was lifted, but the tee-in point could not be located — likely concealed under the concrete kitchen floor.

3. 3
   Pressure test carried out

   Pressure testing equipment was connected to the cloakroom mains. The results confirmed pressure loss, consistent with the findings from the previous visit.

4. 4
   Tracer gas introduced

   Tracer gas was introduced into the system and the mains were emptied via the garage stop tap in preparation for the gas survey.

5. 5
   Tracer gas survey conducted

   A survey of the ground was carried out and high tracer gas readings were detected directly beside the external meter, indicating the likely leak position.

6. 6
   Acoustic testing applied

   Acoustic testing was performed at the location identified by tracer gas, confirming the same spot and providing sufficient confidence to proceed with excavation.

7. 7
   Excavation and leak found

   The area beside the external meter was excavated. The leak was found on a fitting that had been badly cross-threaded during installation, causing it to snap at the thread and fail.

8. 8
   Repair carried out and tested

   The defective fitting was removed and replaced with a 25mm–22mm reducing coupler. The repair was pressure-tested and confirmed sound, and the excavation was backfilled.

Result & Outcome

The leak was located beside the external water meter at the front of the property in SK9. Excavation revealed a fitting that had been badly cross-threaded during its original installation by the water board, causing it to snap at the thread and fail. This was not a case of pipe deterioration or ground movement — the fault was directly attributable to incorrect installation.

The defective fitting was removed and replaced with a 25mm–22mm reducing coupler. A pressure test following the repair confirmed the joint was sound, and the excavation was backfilled. The repair resolves the leak entirely, and the water mains supply is now holding pressure correctly.

For a water mains leak detection job of this type — where the mains route is partially inaccessible and the leak is close to the boundary — the combination of tracer gas and acoustic testing is the most efficient way to arrive at a precise dig location without unnecessary excavation. Given that the fault originated from a water board installation, the customer has been advised to contact the water board to discuss the matter.