Water Mains Leak Detection in Gravesend

Symptoms

The owner of a semi-detached property in DA3 had been receiving abnormally high water bills and called to investigate a suspected underground leak. The property spans two floors, and on arrival there were no visible signs of water damage or damp anywhere inside the building, making it clear the problem was not internal.

Methods Used

Given the confirmed pressure loss and a still-spinning meter with the stopcock closed, the investigation focused on the incoming mains pipework outside the property. Tracer gas was introduced into the pipework to identify where it was escaping to surface — the standard approach for a water mains leak detection job where the leak is underground and not visually apparent.

After the first leak was repaired and a re-test still showed a pressure drop, tracer gas was deployed a second time to confirm whether a further leak was present on the same run of pipe.

Investigation Process

1. 1
   Meter and stopcock check

   The customer showed the engineer the location of the water meter and internal stopcock. With the stopcock isolated, the meter was still spinning, confirming an active leak on the supply side.

2. 2
   Pressure test

   A pressure test was carried out on the mains pipework. Pressure dropped from 2 bar to zero within a couple of minutes, confirming a significant loss in the underground supply.

3. 3
   First tracer gas survey

   Tracer gas was introduced into the pipework and detected escaping at the front of the property on the grass, pinpointing the first leak location.

4. 4
   First excavation and repair

   The front lawn was excavated at the identified point. A pin hole was found in the black alkathene pipe and repaired using a Philmac transition coupling.

5. 5
   Re-test following first repair

   A pressure test was carried out after the first repair. Pressure was still dropping, indicating a second leak remained on the mains.

6. 6
   Second tracer gas survey

   Tracer gas was reintroduced and used to locate the second leak, again on the mains pipework at the front of the property.

7. 7
   Second excavation and repair

   A second excavation was performed and the second leak was repaired using another Philmac transition coupling. Large amounts of rubble and rocks were noted in the excavation.

8. 8
   Final pressure test and meter check

   The water was turned back on. The meter had stopped moving and pressure held stable throughout a one-hour test with no drop recorded.

Result & Outcome

Two separate leaks were located and repaired on the incoming mains pipework at the front of the property in DA3. Both were found on the underground black alkathene pipe beneath the front lawn — the first identified by tracer gas after the initial pressure test, the second confirmed by a further tracer gas survey after re-testing showed pressure was still falling. Both leaks were repaired using Philmac transition couplings, and the final one-hour pressure test showed no pressure drop, with the water meter confirmed stationary.

The presence of large quantities of rubble and rocks in both excavations is a relevant factor for the future condition of this pipe run. As noted in the water mains leak detection findings, if further leaks develop on this section of mains, the ground conditions make a full mains replacement the more practical option rather than additional point repairs. The front lawn will require full reinstatement following the two excavations.