Water Mains Leak Detection in Dunstable

Symptoms

A property in LU6 — a working petrol garage — was losing water continuously, with the meter registering 15 litres per minute of usage while every known outlet was closed. This level of unaccounted flow pointed clearly to a leak on the mains supply rather than any internal fitting or appliance.

The external stop valve was located at the front right of the property, and the suspected mains route ran from that point into the building.

Because the leak was underground and gave no visible surface signs beyond the meter reading, water mains leak detection methods were required to pinpoint it without unnecessary excavation. The combination of continuous meter movement with all outlets shut left no doubt that the mains was breached somewhere between the external stop valve and the internal supply.

Methods Used

Tracer gas was introduced into the mains through the cold supply to the sink, giving the gas access to the full length of the underground pipework. A pressure test was then applied at 2.5 bar, and all pressure was lost almost immediately, confirming a significant breach somewhere along the mains.

The assumed route of the mains was then walked with acoustic listening equipment to detect where the tracer gas was escaping to the surface.

A strong gas trace was detected at a drain cover approximately two metres to the left of the external stop valve. Audible bubbling confirmed the location before the cover was even lifted.

This is exactly the kind of scenario where water mains leak detection with tracer gas proves its value — the leak was underground, within a buried access chamber, and would have been impossible to locate by surface observation alone. Once the cover was removed, multiple leaks were found on a section of mains pipework running through the chamber.

Investigation Process

1. 1
   Meter check and outlet isolation

   With all known outlets on the property closed, the water meter was confirmed to be registering 15 litres per minute, establishing that a live mains leak was present.

2. 2
   Tracer gas introduced

   Tracer gas was fed into the mains through the cold supply to the sink, pressurising the pipework and providing a detectable medium to trace the leak to the surface.

3. 3
   Pressure test applied

   A pressure test at 2.5 bar was carried out on the mains; all pressure was lost almost immediately, indicating a substantial breach in the underground pipework.

4. 4
   Gas trace detected at drain cover

   Walking the assumed mains route with acoustic listening equipment, a large gas trace was detected at a drain cover approximately two metres to the left of the external stop valve, and audible bubbling was clearly heard.

5. 5
   Access chamber opened and inspected

   The drain cover was lifted, revealing an access chamber. Once the chamber was emptied of water, multiple leaks were found on a section of mains pipework running through it.

6. 6
   Leaking pipework cut out and renewed

   The damaged section of mains pipework was cut out and replaced using a transition coupling, a 25mm coupling, 1 metre of 25mm tube, and three 25mm inserts.

7. 7
   Post-repair pressure test and meter check

   The internal and external mains were pressure tested together at 2.5 bar for 30 minutes with no pressure loss recorded. A water meter check confirmed no usage, verifying the repair was complete.

Result & Outcome

Multiple leaks were found on a section of mains pipework inside a buried access chamber, located approximately two metres to the left of the external stop valve. The leaking section was cut out entirely and replaced with new pipework and fittings on the same visit. The access chamber location meant the repair was contained and did not require open excavation of a driveway or footpath.

Following the repair, the internal and external mains were pressure tested together at 2.5 bar for a sustained 30 minutes. No pressure was lost during that period. A water meter check immediately after confirmed zero usage with all outlets closed — a direct contrast to the 15 litres per minute recorded at the start of the job.

For a commercial property in LU6 like this, the result of water mains leak detection that concludes with a same-day repair and a clean pressure test means the supply is restored without any ongoing loss, and without the uncertainty of a leak that has only been partially addressed. The meter movement that prompted the call was completely resolved.