Underground Water Mains Leak Detection in Downham Market

Symptoms

At a property in PE33, the external water meter was observed continuously rotating despite no water being used inside or outside the building. The site has two external taps fed from a single supply — one serving the house and one dedicated to feeding a barn.

All visible pipework inside the barn showed no signs of leakage, pointing firmly to an underground fault somewhere along the buried supply line.

The setup appeared straightforward on the surface: a meter near the main entrance, a tap serving the barn roughly 35 metres away. However, the continuous meter movement with no consumption confirmed an active external leak that warranted proper water mains leak detection to establish exactly where the fault lay.

What made this job more complex than it first appeared was the routing of the supply. Rather than running directly from the meter to the barn, the pipe was found to travel down toward the back fields before returning — a run exceeding 200 metres, far longer than the visible layout suggested.

Methods Used

The investigation began with pressure testing connected to the outside tap serving the barn. At 4 bar of pressure, a drop was recorded within two minutes, confirming an active underground leak on that supply line.

Tracer gas was then introduced through the same connection, and readings were obtained close to the point where the supply rises to feed the external tap and barn — giving a target area for excavation.

As digging progressed, a T-piece with a capped end was uncovered, revealing that the supply route was far more extensive than expected. This kind of methodical, layered approach is what water mains leak detection requires when buried pipework doesn't follow an obvious path.

Excavating deeper exposed the actual leak source: a fitting where the pipe had been reduced from 25mm to 20mm, which had failed.

Investigation Process

1. 1
   Meter and Site Assessed

   The external meter near the main entrance was observed running continuously with no water in use. All visible pipework inside the barn was inspected and found to be leak-free.

2. 2
   Pressure Test Carried Out

   The outside tap feeding the barn was used as the connection point for a pressure test at 4 bar. Pressure dropped within two minutes, confirming an active underground leak on the barn supply.

3. 3
   Tracer Gas Introduced

   Tracer gas was fed into the pipework through the same outside tap connection. Readings were detected at surface level close to where the supply rises near the external tap and barn feed.

4. 4
   Excavation Begun and T-Piece Uncovered

   The flagged area was excavated, revealing a T-piece with one end capped off. This indicated the water mains supply did not run directly to the barn but instead routed down toward the back fields — a total run of over 200 metres.

5. 5
   Leak Located at Failing Fitting

   Digging deeper exposed the source of the leak: a fitting where the pipe had been reduced from 25mm to 20mm, which had failed and was allowing water to escape underground.

6. 6
   Repair Completed and Tested

   The leaking fitting and surrounding pipework were cut out and replaced using 25mm blue poly pipe and two water mains fittings. A follow-up pressure test confirmed the repair was holding with no further pressure loss.

Result & Outcome

The leak was located underground at a failed 25mm-to-20mm reduction fitting on the water mains supply serving the barn. The fault was hidden well below ground level and was only reachable because tracer gas narrowed the search area before excavation began. The leaking fitting and pipework were cut out and replaced with 25mm blue poly pipe and two water mains fittings, with a final pressure test confirming the repair was sound.

One significant finding from this water mains leak detection job was the true routing of the supply. Rather than the expected direct run of around 35 metres from the meter to the barn, the pipe travels down toward the back fields and back — totalling over 200 metres of buried pipework. That extended and indirect route carries a higher risk of future failures.

The engineer has recommended installing a new, direct feed from the meter to the barn at approximately 30 metres. The existing supply to the fields is not operationally necessary, and leaving the long indirect route in place increases the likelihood of further leaks developing in ageing pipework.