Underground Leak Detection in London

We use two non-invasive methods. Acoustic detection involves placing ground microphones and listening rods at intervals along the suspected pipe run and listening for the sound signature of escaping pressurised water. The signal is strongest directly above the failure point. By comparing the signal strength at multiple positions, the engineer triangulates the location.

Tracer gas involves introducing a safe mixture of 95% nitrogen and 5% hydrogen into the isolated pipe section. The gas exits at the failure point and rises to the surface, where a handheld detector sensitive to 1 part per million identifies the exact location.

In most investigations we use both methods in sequence, acoustic first to identify the area, tracer gas to confirm the exact point. No excavation takes place until the failure location has been confirmed.

Acoustic detection typically narrows the failure location to within half a metre in good conditions. Tracer gas confirms the location to within 10-20 centimetres. In combination, the two methods allow us to recommend a targeted excavation area that is as small as possible, which directly reduces the cost of access and reinstatement.

Yes. This is one of the most common reasons customers call us before booking a groundworker. Tracer gas rises through tarmac, block paving and concrete, and we confirm the failure point to within centimetres. That means the minimum possible number of blocks need to be lifted or the smallest possible tarmac cut made. We agree the exact access area with you and confirm the cost before anything is lifted.

Thames Water (or your regional water company) is responsible for the main in the street up to the external stop tap, usually located at or near your property boundary. Everything from the external stop tap to your internal stop tap is the homeowner’s responsibility to maintain and repair. If the leak is in that section, the repair cost falls to you, though it is often covered under buildings insurance trace and access cover.

If you are not sure where your leak sits relative to this boundary, call us on 02080530369. We can advise based on what you describe, and if the failure turns out to be on the water company’s side, we will tell you that clearly.

A standard residential investigation covering a single supply pipe run typically takes between two and four hours. This includes the acoustic scan along the pipe run, the tracer gas introduction and dwell period, and the detection scan. Dwell time varies depending on the depth and density of the material above the pipe. For screed up to 75mm deep, allow 20-30 minutes dwell time. For deeper concrete or dense tarmac, allow longer. The engineer gives you a realistic time estimate on arrival after assessing the specific conditions.

In most cases, yes. For straightforward supply pipe repairs under gardens or paths, our engineers carry out the targeted excavation and repair in the same visit, with a fixed price agreed before any digging starts. For larger excavations, such as a failure beneath a substantial driveway, we agree the full repair scope and cost before starting. If specialist groundwork is required beyond our scope, we will tell you clearly and advise on what to ask for.

Yes, over time. A slow underground leak beneath or adjacent to foundations can erode the soil supporting the structure. This is particularly relevant in London, where many properties are built on clay soil that is sensitive to changes in moisture content. A slow supply pipe leak feeding moisture into clay beneath a foundation can cause differential settlement. If you suspect an underground leak anywhere near your property’s foundations, getting it located and repaired promptly is important.

Yes. Every underground leak investigation includes a written report covering the detection methods used, the equipment specifications, the investigation findings, the confirmed failure location with measurements from reference points on the property, and our repair recommendation. Tracer gas reports also include the pressure test results and the hydrogen detector readings at the confirmed exit point. Reports are delivered within 48 hours and are structured to meet the requirements of the major UK insurers for trace and access claims. Call with your claim reference number for same-day priority.

Yes. The mixture is 95% nitrogen and 5% hydrogen. Nitrogen is completely inert. The hydrogen component at 5% is below the lower flammability limit of hydrogen in open air. The gas is introduced into sealed pressurised pipework, not into the room air, and never accumulates at the surface in concentrations approaching the flammability threshold. The process is safe in occupied residential and commercial properties, including those with gas appliances. Our engineers explain the process fully before starting.