Plymouth, February 2025. A large water bill and a meter still spinning with the internal stopcock off. Tracer gas traced the escape to the mains supply pipe under the stairs. One targeted opening in the concrete, a re-routed cold water supply, and the meter finally stood still.
The problem: a bill that made no sense
The homeowner got in touch after a water bill far beyond anything normal for the house. The classic test confirmed the worst: with the internal stopcock turned off, the water meter outside kept running. Water was escaping somewhere between the meter and the house, underground, with nothing visible anywhere.
This is one of the most common ways a mains leak announces itself, and it is the exact scenario behind many of the letters South West Water sends to households with unusual usage. The water is running under the property day and night, and every litre is on the bill.
Finding it: tracer gas does the talking
Digging up a supply run on guesswork can mean trenching the length of the property. Instead, the supply pipe was charged with tracer gas, a safe hydrogen and nitrogen mix that escapes at the leak point and rises through the ground. Reading where the gas surfaced fastest pointed to one answer nobody would have guessed: the leak was in the section of supply pipe running under the stairs, beneath newer concrete inside the house.
The fix: the cheaper option, recommended in writing
There were two ways out. Replace the whole supply with a new water line, a significant excavation job, or open the concrete at the pinpointed spot and deal with the pipe there. Because the detection had narrowed the leak to one small area, the targeted option was viable, and it was the one we recommended in writing as the cheaper route. The supply was re-routed at that point, the meter stopped, and the homeowner confirmed everything was back to normal, with water usage returned to what it should be.
What this job shows
- A spinning meter with the stopcock off means an underground supply leak. If your bill has jumped, run that test, then read our guide on a high water bill with no visible leak.
- Detection first makes the repair smaller. Pinpointing the leak turned a possible full re-lay into one opening in the right place. That is the whole argument for mains water leak detection before anyone picks up a breaker.
- You should be offered the cheaper option. A good detection report gives you choices, not just a bill.
Got a leak that needs finding?
DCI Leak Detection finds hidden water, heating and pool leaks across Cornwall and Devon using tracer gas, acoustic listening and thermal imaging, with an insurer-ready trace and access report on every job. No find, no fee on residential work, subject to terms.
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