Underground Water Mains Leak Detection in Padstow

Symptoms

A property in PL27 had a suspected leak on the external mains supply. A stopcock isolation test confirmed the leak was on the external mains pipework, which also fed two garden taps connected directly to the mains before the internal stopcock.

The internal stopcock was located in the bathroom at the rear of the property, with the external stopcock situated by the road at the front.

The observed leak rate was approximately 1 litre per minute — a continuous loss that, left unaddressed, would result in significant water waste and potential ground movement or damage to surrounding structures. Water mains leak detection was required to pinpoint the exact location before any excavation could be carried out responsibly.

The challenge on this job was that the leak signal was not straightforward to isolate. Initial acoustic surveys returned nothing significant, and early tracer gas readings pointed toward the rear of the property near the internal stopcock — but subsequent water injection in that area produced no conclusive evidence, meaning further investigation was needed.

Methods Used

The investigation began with a sectional isolation test to establish which section of pipework was losing water. Once the leak was confirmed on the external mains, acoustic equipment was deployed around the property perimeter, but no significant readings were obtained.

Tracer gas was then introduced at 2 bar pressure and detected near the rear of the property close to the internal stopcock entry point. Water was subsequently introduced using a compressor, but the results in that area were inconclusive.

With the customer's agreement, an exploratory excavation was made near the apparent point of entry — no leak was found, but a heavy-duty black membrane was uncovered beneath the slabs, which had likely been masking or deflecting any surface moisture signals. Water and air were reintroduced after this excavation, and a clear leak signal was identified approximately 2 metres further along the side of the house.

This is typical of how water mains leak detection progresses when sub-surface membranes or saturated ground obscure the initial trace — a methodical layered approach is necessary to reach a definitive result.

Investigation Process

1. 1
   Stopcock Isolation Test

   The internal and external stopcocks were used to isolate sections of the supply. The test confirmed the leak was on the external mains pipework, which also supplies the two garden taps fed directly from the mains.

2. 2
   Acoustic Survey

   Acoustic equipment was deployed around the property perimeter to detect any leak noise. No significant readings were obtained at this stage.

3. 3
   Tracer Gas Introduction

   Tracer gas was introduced into the pipework at 2 bar. A reading was detected near the rear of the property, close to where the mains pipe enters at the internal stopcock location.

4. 4
   Water and Air Injection — Inconclusive

   Water was introduced using a compressor to attempt to produce a surface signal at the suspected location near the rear of the property. No conclusive evidence of the leak was found in this area.

5. 5
   Exploratory Excavation — Point of Entry

   With the customer's agreement, slabs near the pipe entry point were lifted and an excavation was carried out. No leak evidence was found, but a heavy-duty black membrane was discovered beneath the slabs.

6. 6
   Reintroduction of Water and Air

   Water and air were reintroduced following the excavation. A clear leak signal was detected approximately 2 metres further along the side of the house.

7. 7
   Leak Visually Confirmed

   The area approximately 2 metres along the side of the property was exposed with the customer's permission. The leak was visually confirmed at this location.

Result & Outcome

The leak was located in the external mains pipework running along the side of the property, approximately 2 metres from the initial excavation point near the pipe entry. The presence of a heavy-duty black membrane beneath the slabs had obscured surface signals and contributed to the misleading initial tracer gas reading near the rear entry point. Once the membrane was exposed and water and air were reintroduced, the true leak position became clear and was visually confirmed.

The leaking section of pipe was excavated and the affected length removed. Because the pipe was of non-standard size, specialist fittings were required. The section was replaced using Blue MDPE, the current standard material for underground mains supply pipework. It was recommended to the customer that the replacement pipe be installed to a minimum depth of 750 mm to provide adequate frost protection going forward.

For water mains leak detection jobs of this type — where sub-surface features complicate signal interpretation — the layered approach of acoustics, tracer gas, and targeted excavation is essential to reach a confirmed result without unnecessary disruption. The precise location was established before the final excavation, keeping groundwork to what was strictly required.