Underground Water Mains Leak Detection in Grantham

Symptoms

The property in NG31 is a large semi-detached house. The water meter had been observed spinning continuously and slowly, indicating water was flowing somewhere in the system even when no appliances or taps were in use.

This is a reliable early indicator of an uncontrolled loss somewhere in the supply pipework.

To confirm the leak was not on the internal cold water system, the internal cold water stopcock was isolated. With the stopcock closed, the meter continued to spin, which pointed clearly to a fault on the external supply pipe between the meter and the property — outside the internal system entirely.

A water mains leak detection survey was the appropriate next step.

Given the age of the property and the presence of old lead pipework on the external main, the leak had likely been running for some time. Left unaddressed, even a slow loss from a failing lead pipe can cause progressive ground movement, wasted water, and eventual supply problems.

Methods Used

The investigation began with a pressure test on the internal cold water pipework to rule out any internal source. The pipework was pressurised to 5.5 bar using an air compressor and held for 30 minutes with no pressure loss recorded, confirming the internal system was intact.

Attention then moved to the external main cold water pipe.

Tracer gas was introduced to the external pipework and the surface above the pipe was systematically surveyed. A positive tracer gas reading was detected on the driveway close to the water meter, and this was corroborated by acoustic evidence picked up at the same location using correlation equipment.

Both methods pointed to the same concentrated area, giving a precise target for excavation. Water mains leak detection work of this kind — combining pressure testing to eliminate internal pipework with tracer gas and acoustic correlation on the external main — is the standard approach when meter evidence points to an underground supply fault.

Investigation Process

1. 1
   Meter behaviour confirmed

   The water meter was observed spinning slowly with no water in use. The internal cold water stopcock was then isolated, and the meter continued to spin, confirming the fault was on the external supply pipe.

2. 2
   Internal pipework pressure tested

   The internal cold water pipework was pressurised to 5.5 bar using an air compressor and held for 30 minutes. No pressure loss was recorded, eliminating the internal system as the source of the leak.

3. 3
   Tracer gas applied to external main

   Tracer gas was introduced to the external main cold water pipe. A positive reading was detected on the driveway surface close to the water meter, indicating the leak was in that area.

4. 4
   Acoustic correlation carried out

   Acoustic equipment was used on the driveway paving near the meter box and confirmed leak noise at the same location identified by the tracer gas, providing a precise target for excavation.

5. 5
   Excavation and fault identified

   The concrete paving slab was lifted and soil excavated. The leak was found on the lead pipe adjacent to the old external stopcock.

6. 6
   Repair completed

   The damaged section of lead pipe was cut out and replaced using a universal transit coupling and short lengths of pipe, restoring the supply.

Result & Outcome

The leak was located on the lead pipe immediately next to the old external stopcock, on the driveway close to the water meter. Both tracer gas and acoustic correlation had independently pointed to this exact area, and excavation confirmed a precise, targeted find. The customer confirmed agreement to proceed with the repair on site.

The damaged section of lead pipe was cut out and replaced with a universal transit coupling and new pipe sections, restoring the supply. For a water mains leak detection job involving old lead pipework, this type of repair resolves the immediate fault, but the condition of the surrounding pipe remains a consideration.

Two recommendations were made following the repair. The external main cold water pipe is old lead and should be replaced in full given its age and condition. Additionally, a pressure reduction valve should be installed on the internal cold water pipework — the water pressure at this property is high enough to place the internal system at risk of future damage.