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The leaks that do the most damage are usually the quiet ones — no flood, no drama, just a small sign that's easy to explain away. Here's what to watch for.
How do we tell if there's a hidden leak? Watch for a damp patch that doesn't dry up, a ceiling stain that keeps spreading, boiler pressure that needs topping up again and again, or a water bill that's climbed for no obvious reason. The clearest test: shut off everything using water, close the stopcock, and see whether your meter keeps ticking. If it does, ring 020 4577 2888 and we'll put you through to a local plumber.
A patch that doesn't dry, a smell that won't shift, a pressure gauge that won't hold, a bill that's crept up. Any one on its own is worth a look; two together is worth a call.
Look for a damp patch on a wall or ceiling that comes back after you've painted over it, or that never quite dries out even in a warm room — that persistence is the tell, because condensation comes and goes with the weather while a leak just keeps feeding itself. A musty smell in a cupboard or under flooring with no visible source is another quiet giveaway, as is a laminate or wood floor that's started to lift or feel soft underfoot near a kitchen or bathroom.
On the mechanical side, a boiler that needs its pressure topped up every week rather than every few months is very often a small leak somewhere in the sealed system, even if you can't see a drop of water anywhere. And a water bill that's risen with no real change in how the house is being used is worth a second look too, particularly on the long rural supply runs out toward Bellarena and Magilligan, where a small loss underground can go unnoticed for a long time.
Turn everything off, close the stopcock, watch the meter. If it's still moving with nothing running, water is escaping somewhere in your system.
Make sure nothing in the house is drawing water — no washing machine mid-cycle, no dishwasher, no tap left dripping — then close the main stopcock fully. If you have a water meter, note the reading and check it again after ten or fifteen minutes without touching anything. A dial that's still crept forward means water is leaving the system somewhere between the meter and wherever it's escaping, even with the stopcock shut, which usually points to the supply pipe itself rather than something inside the house.
If you don't have a meter, the same logic applies with your eyes instead: with the stopcock closed and nothing running, does the damp patch or the drip you've been watching stop? If it keeps going regardless, the leak is likely on the mains side of your stopcock rather than in your own pipework, and that changes who you need to call.
Rule out condensation and rising damp before you assume the worst. Both mimic a leak closely, and neither needs a plumber.
Condensation loves a cold bathroom or a poorly ventilated kitchen, and it tends to spread evenly across a cold surface — a window reveal, an external wall, the corner of a room with little airflow — easing off noticeably once you open a window or run an extractor fan. Rising damp, by contrast, tends to sit low on a wall, near the floor, and often carries a distinctive tide mark rather than the irregular blotch of a leak from above.
A genuine leak usually breaks that pattern: it sits in one persistent, often growing patch, frequently below or beside where pipework runs, and it doesn't improve no matter how much ventilation you throw at it. If in doubt, the stopcock test above settles the question far more reliably than staring at a wall trying to decide.
Inside your walls and under your floor, it's yours. Beyond the boundary, it's NI Water's. The supply pipe in between is the grey area, and usually still yours.
As a rough rule across the UK, everything from your property boundary inward — the pipework inside walls, under floors, feeding your taps and your heating — is the homeowner's to maintain and repair. The public mains beyond that boundary is the water utility's territory, which here in Northern Ireland means NI Water. If you're a tenant, the fixed pipework and heating system are generally the landlord's responsibility to arrange and pay for, though your tenancy agreement is worth checking if you're unsure.
The private supply pipe running from the boundary to the house sits in between, and it's usually still down to the owner, which matters a lot on the longer rural runs around Feeny and Drumsurn where that stretch can cross a field or a lane. A plumber can trace roughly where along the run a leak sits before anyone starts lifting floors or digging up a garden, which saves both money and a great deal of mess.
It's worth ruling out first, especially in a cold bathroom or a poorly ventilated kitchen. Condensation tends to spread evenly, follows cold surfaces like external walls and windows, and eases off with better ventilation. A leak tends to sit in one persistent, growing patch, often below or beside pipework, and doesn't improve however much you open a window.
It's a fair prompt to check, alongside the stopcock test. If your usage has climbed with no real change in habits, a leak somewhere in the supply pipe is a reasonable suspicion, particularly on a long rural run where a small loss can go unnoticed for a long time before it shows up in a damp patch.
Make sure nothing in the house is using water, then close the stopcock fully and watch your water meter, if you have one, for a few minutes. If the dial keeps ticking over with everything off, water is escaping somewhere between the meter and your closed stopcock, or beyond it in your own pipework — either way, it points firmly at a leak rather than a false alarm.
As a rough rule, pipework inside your property boundary is yours to fix, while the public mains beyond the boundary is NI Water's. The supply pipe running from the boundary into your house sits in the middle and is generally still the owner's responsibility. A plumber can help trace exactly where along that run the leak sits before anyone starts digging.
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Read the letter →Pressure drops, no heat, error codes — and gas safety.
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