A Croydon homeowner noticed their water bill had climbed sharply over the previous two quarters, and there was no obvious explanation. No dripping taps, no running toilets, no visible damp indoors. What had caught their eye, though, was a patch of garden that stayed wet and slightly sunken even through a dry spell. They called us to investigate.
This is one of the more common calls we receive for leak detection in Croydon. The combination of a metered supply, an unexplained bill spike, and a boggy garden patch above the supply pipe run points in one direction almost every time.
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The Job: What the Homeowner Called About
The property was a semi-detached house with a front garden separating the boundary from the front door. The homeowner had noticed the wet patch a few weeks earlier but assumed it was drainage. When the water bill arrived, they made the connection. No leaks had been found indoors. The supply pipe ran under the garden from the external stop tap near the pavement edge to the internal stopcock inside the house, and that whole run is the homeowner's responsibility.
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Why the Garden Was the Likely Culprit
Most homeowners are surprised to learn where their responsibility for the water supply actually begins. Thames Water owns the main under the road and the communication pipe running to the boundary. Everything from the external stop tap to the internal stopcock, including the section buried under your garden, belongs to you. If it leaks, you pay to fix it.
In Croydon, that responsibility lands on some of the oldest pipework in London. The borough was largely built out during the Victorian and Edwardian eras, with significant inter-war expansion into the 1930s. Supply pipes in many of these homes are between 60 and 130 years old. Croydon also sits predominantly on London Clay, a geology notorious among engineers for its shrink-swell behaviour. As the clay dries in summer it contracts; as it absorbs winter rain it expands again. Repeated across decades, this ground movement puts cumulative stress on pipe joints and rigid-run connections, and eventually something gives. Thames Water has committed to an ongoing programme of Victorian mains replacement across London, but private supply pipes are outside that remit. They stay the homeowner's problem.
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Confirming the Leak Before Touching a Spade
Before any detection equipment comes out, it is worth performing a simple meter test to confirm the leak is on the supply pipe and not somewhere inside the house.
With the indoor stopcock turned off, we checked whether the meter dials were still moving. They were. That confirmed water was being lost on the supply between the meter and the internal stopcock, somewhere on that garden run. A pressure test then quantified the drop: the pipe was holding significantly less than operating pressure, which ruled out a hairline seep and pointed to a more defined fault point. Importantly, it also ruled out the internal supply as a source, which matters for the insurance claim paperwork later.
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Tracing the Leak Without Excavation
The meter test tells you there is a leak and roughly where on the system it sits. It does not tell you where in the garden to dig. Without detection, the only option would be to open a trench along the full pipe run, disruptive, expensive, and entirely avoidable. Acoustic detection and tracer gas gave us a precise target instead.
Acoustic Detection: Listening Through the Ground
Acoustic detection works by listening through the soil and paving for the vibration signature of pressurised water escaping under stress. A ground-contact microphone was worked methodically along the pipe route, escaping water creates a distinctive noise pattern, a turbulent hiss that resonates through the surrounding ground. As the sensor moved along the run, the signal strengthened noticeably at one point towards the centre of the garden. The acoustic equipment placed the fault within a short section of pipe, narrowing the dig zone to a matter of centimetres.
Tracer Gas: Confirming the Pinpoint
To cross-confirm the location before authorising any excavation, a hydrogen and nitrogen tracer gas mix was introduced into the pipe under low pressure. The gas is inert and non-toxic, and because it is lighter than air it rises through the soil column above the leak point. A detection wand swept across the surface picked up a clear concentration of escaping gas directly above the acoustic hotspot. Two independent methods pointing to the same location is the standard we work to before a spade goes in the ground.
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One Small Excavation, One Confirmed Fix
With the leak pinpointed, a single targeted hole was opened, not a trench across the garden, just enough to expose the affected section of pipe. What we found was a corroded joint, degraded over years of clay ground movement and wet conditions, that had finally failed under pressure.
The joint was repaired, the pipe section pressure-tested with the system repressurised, and the test passed cleanly. The ground was then reinstated. Total disruption to the garden: one small excavation, fully made good.
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What the Homeowner Walked Away With
At the end of the job, the homeowner received a full written survey report documenting the detection process, the methods used, the confirmed leak location, and the repair carried out. That report is what an insurer needs to process a trace and access claim, many buildings insurance policies include trace and access cover, and it is worth checking your policy documents or calling your insurer to confirm whether yours does. Subject to your policy terms and any excess or limits, it typically covers the cost of the investigation and accessing the leak, which may include reinstatement of disturbed ground.
The bill spike was explained: the leak had likely been running for several weeks before the wet patch became noticeable. The homeowner was also advised to contact Thames Water about their leakage allowance scheme, metered customers may be eligible to apply following a confirmed and repaired supply pipe leak, subject to Thames Water's terms and criteria.
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What This Job Shows About Mains Leak Detection in Croydon
This kind of job, a supply pipe failure under a garden, flagged by a bill spike and a persistently damp patch, is not unusual across South London. Victorian and Edwardian housing stock, London Clay ground movement, and the age of private supply pipework combine to make it one of the more common scenarios we deal with across the boroughs.
The outcome here was a single confirmed excavation rather than a speculative trench, a passed pressure test, and an insurance-ready report. That is what non-invasive detection is for. Our engineers are DBS-checked and WaterSafe accredited, we are listed on Checkatrade, and we work across all 32 London boroughs as well as Surrey and Kent. If our detection does not locate a leak, we do not charge for the survey, speak to us about the terms of our No Find No Fee commitment.
If you have a rising water bill and a garden that is not drying out, it is worth getting it checked before the next bill arrives. Call us on 0203 886 2316.