Most water leaks don’t announce themselves. There’s no burst pipe, no water pouring through the ceiling, no dramatic moment where you know something’s wrong.
Instead, there’s a slow, quiet leak somewhere you can’t see, doing damage for weeks or months before anything obvious shows up. By the time most people call our plumbing team in Cardiff, the leak has been running far longer than they realise.
The good news is that hidden leaks almost always leave clues. You just have to know what you’re looking for. Here’s how to tell if you’ve got one.
Your Water Bill Jumps For No Reason
This is the big one, and it’s the sign people most often miss.
If your water usage hasn’t changed but your bill has climbed, water is going somewhere it shouldn’t. A leak doesn’t take a break. Even a slight weep from a pipe that runs every hour of every day adds up fast on a metered supply.
Dŵr Cymru Welsh Water bills most Cardiff homes on a meter, so a hidden leak shows up directly in what you pay. If your latest bill made you do a double take and nothing about your household has changed, that’s worth taking seriously rather than writing off as a one-off.
The Stopcock Test
Here’s a simple check you can do yourself, and it’s the same one we’d start with.
Turn off every tap and water-using appliance in the house. Washing machine, dishwasher, everything off. Then find your water meter and note the reading. Leave it an hour, making sure nobody uses any water at all, then check the meter again.
If the reading has moved, water is flowing somewhere with everything switched off, which means you’ve got a leak. It’s a crude test, but it’s genuinely reliable and tells you whether the problem is real before you call anyone.
Warm Patches On The Floor
This one catches people out because it feels counterintuitive. If you’ve got a hidden leak in a hot water pipe or a central heating pipe running under the floor, the first sign is often a patch of floor that’s warmer than the surrounding area.
People notice it in a kitchen or bathroom, usually with bare feet, and assume it’s just where the sun hits or where a pipe runs normally.
A genuinely warm spot on the floor, especially one that wasn’t there before, can indicate that hot water is escaping beneath the surface. On a tiled floor it’s easy to feel. On carpet it’s harder, but the area may feel damp or spongy underfoot.
The Sound of Running Water When Nothing’s On
Stand still in a quiet house with everything switched off and listen. A faint hiss, a trickle, or the sound of running water when nothing is actually running points to water moving through pipework it shouldn’t be. It’s easiest to hear at night when the house is quiet, or with your ear near the floor or a wall where pipes run.
This is one we rely on ourselves. A lot of leak tracing comes down to listening carefully in the right spots, sometimes with equipment that amplifies the sound, but often just with experience and a quiet room.
Damp, Mould or Musty Smells That Won’t Shift
A hidden leak feeds constant moisture into a space that should be dry, and that moisture has to go somewhere. It shows up as a patch of damp on a wall or ceiling, black mould creeping into a corner that never used to have it, paint or plaster starting to bubble, or simply a musty smell in a room that won’t clear no matter how much you air it out.
The tricky part is that the damp rarely appears directly below the leak. Water travels along joists and pipe runs and comes out at the lowest point it can find, which might be a room away. That’s exactly why a damp patch on a ceiling is so often misdiagnosed, and why cutting into the wall directly behind the stain is usually the wrong first move.
Low Water Pressure That Appeared From Nowhere
If your shower has gone weak or your taps aren’t running like they used to, and nothing else explains it, a leak could be the reason. Water escaping from a pipe before it reaches your taps means less pressure arriving where you want it.
Low pressure has plenty of other causes, so it’s not proof on its own, but combined with any of the other signs here it starts to build a picture.
Cracks, Movement or Damp Around The Foundations
This is the serious end, and it’s rare, but worth knowing. A long-running leak from an underground supply pipe can saturate the ground around your foundations.
In older Cardiff properties, this can eventually show up as damp low down on internal walls or, in extreme cases, as structural movement. If you’re seeing persistent damp at the base of walls with no obvious source, the supply pipe entering the property is worth checking.
What To Do If You Think You’ve Got A Leak
Start with the meter test above. If the meter moves with everything off, you’ve confirmed there’s a leak, and that’s genuinely useful information to have before anyone comes out. If you can, turn the water off at your stopcock when you’re not using it, which at least stops the leak running around the clock while you sort it.
What we’d suggest you don’t do is start pulling up floorboards or cutting into walls to find it yourself. Hidden leaks are genuinely difficult to locate, and the damage from hunting in the wrong place often costs more than the leak itself. Finding a leak without tearing the house apart is a skill, and it’s most of what we actually do on these jobs.
How We Find Hidden Leaks
When we come out to a suspected leak, the aim is to find it with as little disruption as possible. Most of the time we trace a leak and repair it without lifting more than a board or two, because we know where to look first and how to narrow it down. 15 years of doing this across Cardiff means we’ve seen where these leaks tend to hide in local properties, from Victorian terraces with ageing pipework to newer builds where a joint has failed.
Once we’ve found it, we handle the repair too, whether that’s a single joint or a section of pipework that needs replacing. Where a leak has been running long enough to cause damage, quickly identifying the cause is what stops the bill from climbing further.
Think you’ve got a hidden leak? We find and fix water leaks across Cardiff, usually without turning your home upside down. Get in touch, and we’ll come and take a look. If water’s actively coming through, our emergency plumbers can be with you fast.
