Underground Water Mains Leak Detection in Cambourne

Symptoms

The meter was running continuously, indicating water was being lost somewhere across the network. When the plant room isolation valve was closed to shut off the allotment supply, the meter stopped completely — confirming the leak was on that side of the system.

With roughly a mile of pipework involved, pinpointing the exact source required a structured water mains leak detection approach rather than any guesswork or exploratory excavation.

Methods Used

Gas readings emerged around an outside tap on the left-hand side of the allotments. Excavation revealed three separate leaks at that location: two from plastic tee fittings and one from a steel pipe where a bolt was missing.

After the standpipe was replaced and pressure testing repeated, the pressure continued to drop, indicating a second fault. Tracer gas was reintroduced and identified a further leak on a tap in the middle of the rear allotments.

This is standard practice in water mains leak detection — confirming resolution after each repair and continuing until the system holds pressure.

Investigation Process

1. 1
   Meter and isolation check

   The water meter in the car park was observed running continuously. Closing the plant room isolation valve serving the allotments brought the meter to a complete stop, confirming the leak was on the allotment supply.

2. 2
   Pressure test on allotment pipework

   A connection was made to one of the allotment standpipes and the pipework was pressurised to four bar. Within two minutes the pressure had dropped to zero, confirming a substantial leak.

3. 3
   Tracer gas introduced — first leak located

   Tracer gas was fed through the same standpipe connection. Readings emerged at the outside tap on the left-hand side of the allotments, directing excavation to that specific point.

4. 4
   Excavation and first repair

   Three separate leaks were found at the left-hand tap: two from plastic tee fittings and one from a steel pipe where a bolt was missing. The steel standpipe was removed and replaced with a new plastic tap and fittings, using various fittings from 32mm down to 20mm.

5. 5
   Post-repair pressure test — pressure still dropping

   Pressure testing was repeated after the first repair but the pressure continued to fall and the meter was still turning, indicating at least one further leak remained on the system.

6. 6
   Tracer gas reintroduced — second leak located

   Tracer gas was introduced again and identified a second leak at another outside tap in the middle of the rear allotments. This area was marked but not yet excavated at the time of the visit.

7. 7
   System flushed and site left operational

   Water was flushed through the repaired sections to confirm everything was working correctly before leaving site. The customer was advised of the second leak location and will be carrying out the further repair works.

Result & Outcome

It is recommended that all fittings across the allotment supply are replaced with Philmac fittings to reduce the risk of further failures. The site was left with water flowing correctly through the repaired sections, and the customer has a clear scope of works for the outstanding repair.