Water Mains Leak Detection in Hemel Hempstead

Symptoms

A property in HP11 presented with damp appearing on the hallway floor and left-hand side wall. The water meter was registering continuous usage, suggesting water was escaping somewhere within the pipework system, even when no taps or appliances were in use.

Closing the internal stopvalve brought the meter reading to a stop, which confirmed the source of the leak was within the internal pipework rather than the external mains supply. This ruled out the street-side connection as the cause and focused the investigation inward.

For a job of this type, internal leak detection is the appropriate method — systematic pressure testing across each section of pipework, followed by tracer gas and acoustic techniques to pinpoint the exact location without unnecessary disruption to the building fabric.

Methods Used

The investigation began with pressure testing each section of pipework in turn — external mains, internal mains, hot distribution, and cold distribution — to isolate which circuit held the fault. The results confirmed a leak within the internal mains specifically, narrowing the search area considerably.

With the internal mains identified as the problem circuit, tracer gas was introduced and a substantial gas trace was detected in the hallway. Acoustic equipment was then deployed, detecting the sound of escaping water to the left-hand side of the visible damp patch.

This combination of methods is central to internal leak detection work: pressure testing eliminates possibilities, tracer gas confirms the zone, and acoustic correlation identifies the precise point before any excavation begins.

Investigation Process

1. 1
   Initial Assessment

   On arrival, the hallway floor and left-hand side wall were found to be wet. The water meter was confirmed to be registering continuous usage.

2. 2
   Stopvalve Test

   The internal stopvalve was closed, which immediately stopped the meter reading — confirming the leak was within the internal pipework, not the external supply.

3. 3
   Pressure Testing

   The external mains, internal mains, hot distribution, and cold distribution pipework were each pressure tested. The internal mains failed, confirming it as the leaking circuit.

4. 4
   Tracer Gas Introduction

   Tracer gas was introduced into the isolated internal mains. A large gas trace was detected in the hallway, confirming the leak location zone.

5. 5
   Acoustic Detection

   Acoustic equipment was deployed across the hallway area, detecting the sound of escaping water to the left-hand side of the damp patch on the wall.

6. 6
   Excavation and Repair

   The identified area was excavated, exposing the leaking copper pipework. The defective section was cut out and renewed using copper tube and 15mm fittings.

7. 7
   Post-Repair Pressure Test

   The repaired mains was pressure tested at 4 bar for 30 minutes with no loss of pressure recorded, confirming the repair was sound.

8. 8
   Meter Verification

   A 15-minute meter check was carried out with all isolation valves open. No usage was registered during this period, confirming no remaining leaks.

9. 9
   Stopvalve Recommendation

   The packing gland on the internal stopvalve was found to be dripping. A temporary repair was carried out on the valve, with a recommendation that it may need full replacement in the near future.

Result & Outcome

The leak was located in the hallway, to the left-hand side of the visible damp patch on the wall. Excavation at that point exposed the defective copper pipework, which was cut out and replaced with new copper tube and 15mm fittings. A post-repair pressure test at 4 bar held for 30 minutes without any pressure loss, and a subsequent meter check over 15 minutes showed no further usage — both confirming a complete and effective repair.

For the occupants, this outcome means the source of the damp and the unexplained water consumption has been fully resolved. The precise location method used in this internal leak detection job meant excavation was targeted directly at the fault, avoiding unnecessary disruption to the surrounding hallway area.

One additional finding was noted: the packing gland on the internal stopvalve was dripping. A temporary repair was carried out on site, but the valve may require full replacement in the near future to prevent it becoming a further source of water loss.