Underground Water Mains Leak Detection in Bidford-on-Avon

Symptoms

A property in B50 was experiencing water seeping up through the lawn, indicating a leak somewhere on the underground supply pipework. The visible wet ground was the first sign that something was wrong beneath the surface, though the exact source and location of the fault needed confirmation through systematic testing.

Water mains leak detection is the appropriate response when surface flooding of this kind points to a pressurised underground supply pipe. Without investigation, a leak on the external cold mains can continue undetected, causing ongoing water loss and potential ground movement.

The task was to isolate which section of pipework was affected, locate the precise failure point, and carry out a repair.

Methods Used

The investigation followed a staged approach: flow testing to confirm a leak existed, pressure testing to isolate which section of pipework was failing, and tracer gas to pinpoint the exact location underground. The internal cold mains was pressure tested first to rule it out, passing at 4.5 bar over 20 minutes.

The external cold mains failed its pressure test under the same conditions, confirming the fault was outside the property boundary.

Tracer gas was then introduced into the external pipework. The gas surfaced in the same area where the lawn was already flooding, giving a precise location for excavation.

This staged approach — pressure testing to isolate, tracer gas to locate — is standard practice in water mains leak detection and avoids unnecessary excavation across a wider area.

Investigation Process

1. 1
   Initial visual inspection

   On arrival, water was observed seeping up through the lawn, indicating a possible underground leak on the external supply.

2. 2
   Flow test at meter

   A flow test was carried out at the water meter with the internal stopcock closed. Flow was still present, confirming an active leak on the external cold mains.

3. 3
   Pressure test — internal cold mains

   The internal cold mains was pressure tested at 4.5 bar for 20 minutes. It passed, ruling out any internal pipework fault.

4. 4
   Pressure test — external cold mains

   The external cold mains was pressure tested at 4.5 bar for 5 minutes. It failed, confirming the leak was on the external supply pipe.

5. 5
   Tracer gas investigation

   Tracer gas was introduced into the external cold mains. Gas was detected rising from the ground in the same location where the lawn was flooding, pinpointing the leak.

6. 6
   Excavation and fault found

   Excavations were carried out at the identified location. A large rock was found rubbing against the external 28mm black alkathene cold mains pipe, causing the failure.

7. 7
   Materials collected and repair carried out

   Materials were collected from a local supplier. The damaged section of 28mm black alkathene mains was repaired using a 28mm transition coupling.

8. 8
   Post-repair pressure test

   The external cold mains was pressure tested again at 4.5 bar for 20 minutes. It passed, confirming the repair was sound.

9. 9
   Final flow test and backfill

   A final flow test at the water meter showed no flow, confirming the leak had been resolved. Excavations were then backfilled.

Result & Outcome

The leak was found on the external 28mm black alkathene cold mains pipe, caused by a large rock bearing against the pipe underground and wearing through it over time. The location was confirmed precisely by tracer gas surfacing at the same point where the lawn had been flooding, meaning excavation was targeted directly at the fault with no guesswork involved.

The damaged section was repaired using a 28mm transition coupling, with materials sourced locally on the day. A post-repair pressure test at 4.5 bar held for 20 minutes, and a final flow test at the meter showed no residual flow with the system restored to normal operation. The repair was completed and excavations backfilled before leaving site.

For water mains leak detection cases like this, confirming zero flow at the meter after repair is the clearest indicator that the leak has been fully resolved. The recommendation to monitor the water meter for excessive usage going forward is a sensible precaution to detect any future issues early.