The clearest signs of a hidden water leak are a water meter that keeps moving when everything is off, a rising water bill with no change in use, a warm or damp patch on a floor or wall, a musty smell, and a boiler that keeps losing pressure. One sign alone can have another explanation. Two or more together are a strong reason to book a leak detection survey.
Most hidden leaks don’t announce themselves with a puddle. They show up as a slightly higher bill, a faint smell that wasn’t there last month, or a floor that feels warmer in one spot than it should. This page works through ten signs worth checking for, roughly in order of how reliable each one is on its own, so you can build a picture rather than chase a single clue. If you’ve already spotted something and want the practical next step, see our guide to how to find a water leak.
On this page
- 1. A water meter that keeps moving
- 2. An unexplained rise in your water bill
- 3. A boiler or system that keeps losing pressure
- 4. Warm or damp patches on floors
- 5. A musty or damp smell
- 6. Stains on ceilings or walls
- 7. The sound of running water with everything off
- 8 to 10. Flooring, paint and garden signs
- What to do if two or more signs are present
- Hidden leaks in Cornwall & Devon homes
- Frequently asked questions
1. A water meter that keeps moving
This is the single most reliable check available to any homeowner. Turn off every tap, appliance and outside tap that uses water, note your meter reading, wait around two hours without using any water at all, then check the reading again. Any movement means water is passing through the meter somewhere on your supply, even with nothing deliberately running. Our guide to high water bill, no visible leak covers this test in more detail, along with the other hidden causes worth ruling out first.
2. An unexplained rise in your water bill
A leak, particularly a slow one on a private supply pipe, can run for weeks or months before it becomes visible inside the property. A bill that’s noticeably higher than the same period last year, with no real change in household water use, is often the earliest warning sign available, arriving well before any physical symptom.
3. A boiler or system that keeps losing pressure
Needing to top up your central heating’s filling loop more than occasionally suggests water is leaving the sealed system somewhere. It might be a straightforward cause such as a faulty pressure relief valve or expansion vessel, or it might be a pipe leaking under a floor or behind a wall. Our guide to how to increase boiler pressure explains the correct top-up process and the point at which repeated top-ups become a red flag rather than routine maintenance.
4. Warm or damp patches on floors
A patch of flooring that feels warmer than the rest of the room, particularly if there’s no heating pipe run supposed to be underneath it, often means hot water is escaping nearby and warming the floor from below. A cold water leak produces a similar effect with damp rather than warmth, sometimes felt as a slightly spongy or soft patch on carpet, or discolouration on laminate or vinyl.
5. A musty or damp smell
A persistent musty smell in one part of a room, especially one that wasn’t there before, can mean moisture is trapped somewhere it shouldn’t be. On its own this could be poor ventilation or ordinary condensation. Combined with a warm patch, a stain, or meter movement, it becomes a much stronger indicator of a leak.
6. Stains on ceilings or walls
A yellow-brown stain on a ceiling below a bathroom, or a damp patch spreading across a wall near pipework, is one of the more obvious signs, though by the time it appears the leak has usually been running for a while. A stain that keeps returning after decorating, rather than a one-off mark from a past event, points to an ongoing source rather than historic damage. Our guide to water stain came back after repair covers what it means when a mark reappears.
7. The sound of running water with everything off
Hearing water moving through pipes, in a wall or under a floor, when every tap and appliance is switched off is a strong sign worth acting on. It suggests water is actively flowing somewhere it shouldn’t be, rather than sitting as a slow, static seep.
8 to 10. Flooring, paint and garden signs
A handful of further signs round out the picture, each more reliable in combination with the ones above than alone.
- Flooring changes: laminate lifting at the joints, tiles sounding hollow when tapped, or carpet that feels persistently damp in one spot.
- Bubbling or peeling paint, particularly on a wall near known pipework, where moisture is pushing through from behind the surface.
- An unusually green or lush patch of lawn, or soft, boggy ground in one area, which can indicate a leak on an underground supply pipe running through the garden.
What to do if two or more signs are present
One sign alone often has an innocent explanation. Two or more appearing together, particularly a meter that moves with everything off plus any physical symptom, is when a hidden leak becomes the more likely answer rather than a possibility to rule out later.
| Combination of signs | What it suggests |
|---|---|
| Meter movement + rising bill | Active leak somewhere on the supply pipe |
| Warm floor patch + falling boiler pressure | Likely central heating pipe leak |
| Musty smell + recurring stain | Ongoing leak rather than historic damage |
| Green lawn patch + higher bill | Possible leak on the underground supply pipe |
At that point, professional water leak detection and thermal imaging leak detection can confirm the source using non-invasive equipment, thermal cameras, acoustic sensors and correlators, and tracer gas where needed, before anything needs to be opened up. If you’re already dealing with an insurance claim, our guide to leak detection cost UK sets out what typically influences pricing.
Hidden leaks in Cornwall & Devon homes
Across Cornwall and Devon, granite cottages, cob-built properties and converted barns often have solid walls and solid floors that hide pipework completely, so several of the signs above, especially a warm patch or a musty smell, are frequently the only early clue available. Coastal exposure and the region’s mild, wet climate also mean background dampness is higher than the UK average, which makes it easy to dismiss a genuine leak as "just an old house". We see this pattern most weeks: a homeowner who has lived with a slightly damp corner for years turns out to have a leak that’s been running quietly the whole time. If two or more signs from this page apply to your property, it’s worth having them checked rather than assumed.
Frequently asked questions
What is the most reliable sign of a hidden water leak?
A water meter test is usually the most reliable single check. Turn off every tap and appliance that uses water, note the meter reading, wait around two hours without using any water, then check again. Any movement on the meter during that time means water is escaping somewhere on your supply.
Can a hidden water leak affect my water bill before I see any damage?
Yes. A leak inside a wall, under a floor, or underground on a private supply pipe can run for weeks before any staining, damp patch or damage becomes visible. An unexplained rise in your water bill is often the first sign, arriving well before any physical symptom in the property itself.
Is a musty smell always a sign of a leak?
Not always. Poor ventilation, condensation and general damp in an older property can all produce a musty smell without an active leak. It becomes a stronger signal when the smell is localised to one area, is new, or appears alongside other signs such as a warm patch, a stain, or a meter that keeps moving when everything is turned off.
Who is responsible for a hidden leak in my pipes, me or the water company?
In the South West, South West Water is responsible for the mains up to the boundary or stop tap, while the homeowner is responsible for the private supply pipe running from that point into the home. A leak on your side of the boundary is your responsibility to have found and repaired, though South West Water runs a leak allowance scheme for metered customers in some circumstances.
Will my home insurance cover a hidden water leak?
Escape of water is usually covered as standard under buildings insurance, according to the Association of British Insurers. Trace and access cover, highlighted by price-comparison service Confused.com as typically covering up to around £5,000, pays for finding the leak and repairing the damage caused by the search, though not the pipe repair itself. Check your own policy for the exact limits.
How is a hidden leak found without digging up the garden or lifting the floor?
Non-invasive methods narrow the leak to a small area before anything is disturbed. Thermal imaging picks up the warm or cool signature water leaves behind, acoustic sensors and correlators listen for the sound of water escaping under pressure, and tracer gas, a safe mix of 5% hydrogen and 95% nitrogen, can be detected at the surface with a sensitive probe.
When should I call a professional rather than keep checking myself?
If a meter test confirms water is moving with everything off, or two or more of the signs on this page appear together, that’s the point to book a survey rather than keep investigating alone. The longer a hidden leak runs, the more damage and cost it tends to cause, so acting on a confirmed sign promptly is usually worthwhile.
Two or more signs sounding familiar? Let’s confirm what’s happening
If your meter’s moving, your bill’s climbing, or you’ve spotted a warm patch or a smell that won’t go away, we’ll trace the source across Cornwall & Devon with non-invasive equipment and document it for your insurer if needed.
Call Dickie on 07822 025 911 No Find, No Fee on residential leak detection (subject to terms)