Underground Water Mains Leak Detection in Derby

Symptoms

A property in DE11 was experiencing high water consumption, with concern that the external supply had developed a further leak — a previous leak had already been found and repaired on the same run. The external meter sits on a grass verge adjacent to the driveway entrance, with the supply running up the drive to feed the internal riser at the rear of the property.

The presence of a historical repair patch on the driveway tarmac added weight to the suspicion that the external pipework was the source of the problem.

The situation required a methodical approach to confirm whether the leak was external or internal, quantify the loss rate, and pinpoint the exact location without unnecessary excavation. For a water mains leak detection job of this nature — involving an older lead supply with a prior repair history — the risk of failure at a transition point was a key consideration from the outset.

Until the source was identified and isolated, the uncontrolled water loss was ongoing, with no straightforward way for the occupant to prevent it without shutting off the supply entirely.

Methods Used

Flow metering established the baseline loss rate and, critically, confirmed the leak was on the external run by showing no change when the internal supplies were isolated. A pressure test using tracer gas at three bar produced an instant pressure loss, confirming an active leak on the external pipework.

The investigation then moved to locating the precise point of failure without opening up the ground unnecessarily.

A specialist gas analyser was used to sweep the full length of the external run. Elevated gas readings concentrated around the historical tarmac repair patch indicated the likely area, and acoustic profiling was used to corroborate those readings — both methods independently raised concern at the same location.

This dual-method confirmation is standard practice in water mains leak detection where a precise excavation point needs to be justified before ground is broken. With agreement from the client, a targeted excavation was carried out at that specific point.

Investigation Process

1. 1
   Meter monitoring

   Flow metering recorded an uncontrolled usage rate of one litre every 90 seconds. The rate remained identical with all internal supplies isolated, confirming the loss was on the external supply.

2. 2
   Tracer gas pressure test

   A pressure test was conducted using tracer gas at three bar. An instant pressure loss confirmed an active leak on the external run.

3. 3
   Gas analyser sweep

   A specialist gas analyser was used to sweep the full external supply route. High gas readings were recorded concentrated around a tarmac patch covering a historical repair.

4. 4
   Acoustic profiling

   Acoustic profiling was carried out across the same area. The results corroborated the gas readings, independently raising a concern directly below the repair patch.

5. 5
   Excavation

   With client agreement, a targeted excavation was carried out at the identified location. This exposed two transition couplers where the connection to the original lead supply had failed, with significant deterioration visible on the lead pipe at the connection point.

6. 6
   Repair

   The deteriorated lead pipe was cut back past the damaged section and a new transition coupler was installed.

7. 7
   Post-repair pressure test

   A second tracer gas pressure test was conducted at four bar — one bar above mains pressure. No pressure loss was recorded and meter activity ceased, confirming the supply was sound.

Result & Outcome

The leak was located beneath the tarmac patch on the driveway, at the point where two transition couplers connected to the original lead supply. One of those connections had failed, and the lead pipe itself showed significant deterioration at the joint. The location corresponded precisely with the area flagged by both the gas analyser and acoustic profiling.

The damaged section of lead pipe was cut back and a new transition coupler was fitted. A post-repair pressure test using tracer gas at four bar — one bar above mains pressure — confirmed no further pressure loss and no uncontrolled meter activity. The supply was verified as sound before the excavation was backfilled.

The outcome for this water mains leak detection job carries a forward-looking consideration: the supply is the original lead pipework, and with one prior repair already on record plus significant deterioration found at this connection point, any further leaks may make full supply replacement the more practical course of action. New tarmac covering over the repaired area will also be required.