Underground Water Mains Leak Detection in Sheffield

Symptoms

A property in S9 was experiencing elevated water consumption, prompting suspicion of a leak on the underground supply. A meter was located on the public footpath at the driveway entrance, with an internal stopcock accessible in the basement.

Initial testing with the internal stopcock turned on for half an hour showed consistent meter usage, pointing to an active leak on the external supply pipe between the meter and the building.

The concern was that an uncontrolled loss of this kind, if left unaddressed, would continue to drive up consumption with no visible signs above ground. Water mains leak detection was required to identify the precise source before any excavation could be justified.

With the external supply running unseen beneath a front garden and driveway, pinpointing the fault without disruptive guesswork required specialist equipment and a structured approach.

Methods Used

The investigation began by confirming the leak was external using flow metering at the street meter, with the internal stopcock isolated. Acoustic profiling was then carried out, which raised a concern in the vicinity of the internal stopcock.

To narrow the location further, tracer gas was purged into the pipework and a full sweep of the site was conducted using a specialist gas analyser, identifying a zone of high gas emission in the front garden close to the edge of the driveway.

A trial excavation in the grassed area exposed the mains supply and revealed a leak at a transition fitting where the 25mm MDPE reduced to 15mm copper. After reseating and tightening that fitting, a pressure test indicated further loss.

The MDPE pipe was then tracked under the driveway, where a secondary leak — a small crack in the pipe — was located and repaired. This kind of layered approach is typical of water mains leak detection where multiple faults can exist on a single supply run.

Investigation Process

1. 1
   Meter test with stopcock isolated

   With the internal stopcock turned off, the street meter was monitored and showed consistent usage at approximately one litre in just over 30 seconds, confirming the leak was on the external supply.

2. 2
   Acoustic profiling conducted

   Acoustic equipment was deployed across the supply route. A notable concern was raised in the area close to the internal stopcock.

3. 3
   Tracer gas introduced and site swept

   Tracer gas was purged into the pipework and a full sweep of the property was carried out with a specialist gas analyser. High readings were detected in the front garden, close to the edge of the driveway.

4. 4
   Trial excavation in grassed area

   An excavation was made in the grassed area of the front garden, exposing the mains supply and revealing a leaking transition fitting where the 25mm MDPE pipe reduced to 15mm copper.

5. 5
   First fitting reseated and pressure tested

   The transition fitting was reseated and tightened. A subsequent pressure test showed further pressure loss, indicating an additional fault remained on the supply.

6. 6
   Secondary leak located under driveway

   The MDPE pipe was tracked under the driveway where a small crack in the pipe was identified as the source of the secondary leak.

7. 7
   Cracked section removed and repaired

   The cracked section of MDPE pipe was removed and repaired using a 25mm MDPE coupler.

8. 8
   Final pressure test confirms integrity

   A final pressure test recorded no further loss, and no uncontrolled usage was present at the meter, confirming the supply was fully restored.

Result & Outcome

Two separate faults were identified and repaired on the external mains supply at the property in S9. The first was a leaking transition fitting where 25mm MDPE reduced to 15mm copper, located in the front garden close to the driveway edge. The second was a cracked section of 25mm MDPE pipe running beneath the driveway itself. Both were confirmed through staged pressure testing, which showed remaining loss after the first repair and a clean result only once the second repair was complete.

The cracked pipe section was removed and replaced using a 25mm MDPE coupler. With no further pressure loss recorded and no uncontrolled usage visible at the street meter, the integrity of the supply was confirmed. This is the standard of proof required to close a water mains leak detection case — zero movement on the meter under controlled conditions.

The engineer has recommended that soft sand be used to bed the pipe before backfilling the excavations, protecting the repaired MDPE from damage during reinstatement.