Underground Water Mains Leak Detection in Gloucester

Symptoms

A property in GL5 had a suspected leak on the cold water mains supply. The first indication came at the water meter, where flow was still registering even after the internal stopcock was turned off — pointing clearly to a fault on the external supply rather than anywhere inside the building.

With the leak isolated to the external cold mains, a water mains leak detection investigation was required to pinpoint the exact location before any excavation could take place. The leak was not visible at the surface, and the pipe ran beneath a concrete courtyard, making non-invasive detection methods essential.

Left unaddressed, a leak of this kind leads to continuous water loss, potential damage to surrounding ground and structures, and ongoing unmetered usage costs.

Methods Used

The investigation began with flow and pressure testing to confirm which section of pipework was responsible. The internal cold mains passed a 2 bar pressure test over 15 minutes, ruling it out.

The external cold mains failed a 2 bar pressure test after 5 minutes, confirming the leak was outside. Tracer gas was then introduced to the external pipe and gave a strong reading in the concrete courtyard adjacent to a drain cover.

Acoustic investigation at the same location produced a consistent high reading, corroborating the tracer gas result.

For water mains leak detection in situations like this — where a buried pipe runs beneath a concrete surface — combining tracer gas with acoustic methods significantly narrows the excavation target. Both tests pointed to the same spot, giving enough confidence to proceed with a targeted excavation rather than any speculative digging.

Investigation Process

1. 1
   Flow test at meter

   A flow test was carried out at the water meter with the internal stopcock turned off. Flow was still present, indicating the leak was on the external cold mains.

2. 2
   Pressure test — internal cold mains

   A pressure test was applied to the internal cold mains at 2 bar for 15 minutes. The test passed, ruling out any internal pipework.

3. 3
   Pressure test — external cold mains

   A pressure test was applied to the external cold mains at 2 bar for 5 minutes. The test failed, confirming the fault was on the external supply.

4. 4
   Tracer gas investigation

   Tracer gas was introduced to the external cold mains. A high reading was detected in the concrete courtyard adjacent to a drain cover.

5. 5
   Acoustic investigation

   Acoustic equipment was used in the same area of the courtyard, producing a high reading consistent with the tracer gas result.

6. 6
   Excavation and fault found

   The concrete courtyard was excavated at the location indicated by both tests. A conversion joint from 15mm copper to 25mm MDPE was exposed and found to be poorly installed and leaking.

7. 7
   Materials collected and repair carried out

   Materials were collected from a local supplier. On return, the faulty joint was replaced using a 25mm x 15mm transition coupling, a 25mm MDPE coupling, and a short piece of 25mm MDPE pipe.

8. 8
   Post-repair pressure test

   A pressure test was carried out at 4.2 bar for 10 minutes following the repair. The test passed.

9. 9
   Post-repair flow test

   A final flow test was carried out at the water meter. No flow was recorded, confirming the leak had been resolved.

10. 10
    Excavation backfilled

    The excavation in the concrete courtyard was backfilled on completion.

Result & Outcome

The leak was traced to a conversion joint in the concrete courtyard, where a transition from 15mm copper to 25mm MDPE pipe had been poorly installed. The joint was leaking continuously, accounting for the flow reading at the meter. Both tracer gas and acoustic testing independently identified the same location, allowing the excavation to be targeted precisely.

Following repair with a new transition coupling and a short section of 25mm MDPE pipe, the system held at 4.2 bar for 10 minutes and the meter showed no further flow — a clean result. The precision achieved here is what water mains leak detection is designed to deliver: a confirmed fault location before any ground is broken, minimising the size and disruption of the excavation.

The recommendation going forward is to monitor the meter for any further excessive usage, in case there are additional issues elsewhere on the supply.