Underground Water Mains Leak Detection in Plymouth

Symptoms

A property in PL4 had a leak on its incoming mains supply that required further trace and access work to fully locate and resolve. The leak was situated on the lead mains riser running between the closet WC and the outside wall — a section of pipework that was not immediately accessible without targeted investigation and physical exposure of the line.

The nature of the leak meant that standard visual inspection alone was not sufficient. The lead riser passed beneath floor coverings, garden decking, concrete, and brickwork, making precise localisation essential before any excavation or repair work could begin.

A water mains leak detection approach combining acoustic and tracer gas methods was required to narrow the fault area with enough confidence to justify breaking ground.

Once the leak area was confirmed, the condition of the pipework was clear — the 3/4 inch lead mains riser had failed and needed to be re-piped in full, from the garden through the outside wall and into the closet WC housing the internal riser.

Methods Used

On arrival, acoustic testing was carried out on the incoming mains supply to begin narrowing down the leak area. The mains supply was then isolated and tracer gas was introduced into the pipework to carry out additional localisation.

Combining both methods pinpointed the leak area to just in front of the outside wall and from the closet WC — confirming the fault lay on the lead mains riser in that section.

This combined approach is standard practice in water mains leak detection where pipework runs beneath solid or covered surfaces. Once the location was confirmed with sufficient precision, the floor beneath the WC was exposed, two sections of garden decking were removed, and concrete and brickwork were excavated to reach the failed pipe.

Pressure testing at 4.0 bar over one hour was used to verify the integrity of the completed repair.

Investigation Process

1. 1
   Acoustic testing on arrival

   On arrival, the incoming mains supply was acoustically tested to begin localising the leak area along the riser.

2. 2
   Mains isolated and tracer gas introduced

   The mains supply was isolated and tracer gas was added to the pipework to carry out further localisation alongside the acoustic results.

3. 3
   Leak area pinpointed

   With both tests combined, the leak was localised to the area just in front of the outside wall and from the closet WC, identifying the fault as being on the lead mains riser between those two points.

4. 4
   Access excavation carried out

   The WC floor was exposed and two sections of garden decking, concrete, and brickwork were removed to excavate down to the failed 3/4 inch lead mains riser.

5. 5
   Failed lead riser exposed and confirmed

   Excavation revealed a failed 3/4 inch lead mains supply on the riser running beneath the outside wall.

6. 6
   Mains riser re-piped

   A new 20mm blue poly pipe was run from the garden, under the outside wall, and into the closet WC housing the internal riser, using two transition fittings to adapt to the existing supply.

7. 7
   Pressure test completed

   The repaired mains supply was tested at 4.0 bar of tracer gas over one hour with no drop in pressure recorded — all passed.

8. 8
   Customer advised on insurance

   The customer was advised to send the report to their insurers, as all works fall under the trace and access provision of their buildings insurance policy.

Result & Outcome

The leak was located on the 3/4 inch lead mains riser between the closet WC and the outside wall at the property in PL4. The combination of acoustic correlation and tracer gas provided the precision needed to direct excavation to exactly the right area, avoiding unnecessary disruption elsewhere on the site.

Once exposed, the failed lead pipe was confirmed and the entire riser section was re-piped using 20mm blue poly with transition fittings to connect to the existing supply at both ends. Pressure testing at 4.0 bar held for a full hour with no pressure drop, confirming the repair was sound. For a water mains leak detection job involving buried lead pipework beneath decking and concrete, this result — precise location, targeted excavation, and a verified repair — represents a complete resolution.

The customer has been advised to submit the engineer's report to their insurers. The works are covered under the trace and access clause of their buildings insurance policy, meaning the investigation and repair costs should be met through the claim.