Most water leaks do not announce themselves. There is no puddle, no dripping tap, no obvious disaster. Instead a pipe behind a wall or under a floor lets go a small amount of water every hour, and it keeps doing that for weeks before anyone notices.
By the time you see a stain on the ceiling, the water has usually been travelling for a long time. Plaster, joists, insulation and flooring soak it up quietly. That is why leaks that took two hours to fix end up costing thousands to put right.
Here are the five signs worth paying attention to.
1. Your water bill jumps and nothing has changed
You have not filled a paddling pool. Nobody has moved in. Your habits are the same as last quarter. But the bill has gone up.
A leak the width of a pinhole can waste hundreds of litres a week. It never shows on the floor because the water soaks straight into the ground or the building fabric. Compare your last four bills. If usage has climbed steadily while your household has stayed the same size, something is running that should not be.
Some London water companies offer a leak allowance if you can show the leak was hidden and you fixed it promptly. Keep the paperwork.
2. Your water meter moves when nothing is switched on
This is the simplest test you can do yourself and it takes about half an hour.
- Turn off every tap in the property. Switch off the washing machine and dishwasher. Do not flush anything.
- Find your water meter. In most London properties it sits in a small chamber near the boundary of the pavement, under a plastic cover.
- Write down the reading, including the red dials or the last digits.
- Wait 30 to 60 minutes without using any water at all.
- Read it again.
If the number has moved, water is leaving the system somewhere. You have a leak.
If you want to narrow it down, turn off your internal stopcock and repeat the test. Meter still moving means the leak sits between the meter and the house, usually on the supply pipe. Meter now still means the leak is inside the property.
3. Damp patches, bubbling paint or a musty smell
Water travels along joists and pipe runs before it drops. A damp patch in the hallway ceiling might come from a leak in the bathroom two rooms away. That is why chasing the stain rarely works.
Look for paint that has started to bubble, wallpaper lifting at the seam, skirting boards that feel soft, or tile grout that has darkened. A musty, earthy smell in a room with no obvious damp is worth taking seriously. Mould needs moisture, and moisture that has no visible source usually comes from a pipe.
Anything that smells damp after a dry fortnight is a leak until proven otherwise.
4. Your boiler keeps losing pressure
Top up the pressure, watch it drop again over a week, top it up again. Plenty of people do this for months.
A sealed heating system does not lose water on its own. If the pressure gauge falls, water is escaping somewhere. Sometimes the cause is the pressure relief valve discharging outside through a copper pipe on an external wall. Sometimes it is a corroded radiator valve or a pinhole in a pipe buried in a screed floor.
Check the radiator valves and under the boiler first. If everything looks dry, the leak is hidden. Call someone before the constant refilling introduces fresh oxygen into the system and corrodes it from the inside. Our boiler and heating engineers deal with this most weeks.
5. You can hear water running when nothing is on
Stand in a quiet room late in the evening. Turn off the boiler and the taps. Listen.
A faint hiss, a trickle, or a low rushing sound inside a wall means pressurised water is escaping through a small gap. The sound carries a long way through copper. You might hear it in the bedroom while the actual leak sits under the kitchen floor.
Do not ignore it because you cannot see anything. That noise is the earliest warning you will get.
One more sign worth knowing about
If part of a floor feels noticeably warmer than the rest, and you have underfloor heating or hot water pipes running below, you may have a hot water leak. Warm patches on tiles or laminate almost always mean escaping hot water. These leaks do the most damage because they run continuously and dry the surrounding timber unevenly.
What to do the moment you suspect a leak
Turn off the water at the stopcock. In most London flats and terraces you will find it under the kitchen sink, in an airing cupboard, or near the front door. Turn it clockwise until it stops. If you cannot find it, ring us and we will talk you through where to look.
Then take photographs of any damage before you touch anything. Insurers ask for these.
Do not start pulling up floorboards or knocking off plaster. People do this hoping to find the source and end up opening the wrong wall. It makes the repair bigger and the insurance claim messier.
How we find leaks without wrecking your house
Guesswork costs money. We use equipment instead.
Thermal imaging cameras read temperature differences across a surface. Water changes how a wall or floor holds heat, so a hidden leak shows up as a shape on the screen before anything is visible to the eye.
Acoustic listening devices pick up the sound of water forcing its way through a tiny gap in a pressurised pipe. Amplified, that sound is distinct and traceable.
Moisture meters map how far the water has spread, which tells us where the leak is and where it is not.
We combine all three, pinpoint the source, then open up one small area rather than several large ones. Repair, make good, done. That whole process is called trace and access and it starts from £250 plus VAT.
Will your insurance pay for it
Most UK home insurance policies cover trace and access as a specific benefit, often up to a set limit. The policy pays to find the leak and repair the damage the water caused. The pipe repair itself is sometimes covered and sometimes not, depending on the wording.
Read your policy schedule. Look for the words trace and access. If you find them, ring your insurer before work starts and tell them what is happening.
We produce the reports and photographs insurers ask for, and we deal with them directly if you would rather not.
When to call a plumber and when to wait
Call straight away if water is visible, if a ceiling is sagging, or if the leak is anywhere near electrics. Sagging plaster full of water is heavy and it comes down without warning.
For a slow leak with no visible water, book a leak detection visit in the next few days. Waiting a week rarely makes the leak worse. Waiting three months usually does.
If it is the middle of the night and water is coming through the ceiling, that is what our 24 hour emergency line exists for. Ring 020 7247 9304.
Frequently asked questions
How long can a hidden leak run before it causes damage?
Timber starts to rot at sustained moisture levels above roughly 20 percent. A slow leak reaches that within a few weeks. Damage to plaster and decoration often appears well before that.
Can I find a leak myself?
You can narrow it down with the meter test and the stopcock test described above. Finding the exact location without thermal or acoustic equipment usually means opening up walls and floors, which costs more than the detection would have.
How much does leak detection cost in London?
Our trace and access service starts at £250 plus VAT, covering detection, access, repair and making good. Straightforward leak repairs are charged at our plumber rate. See the full pricing page.
Does a leak affect my neighbours if I live in a flat?
Often, yes. Water travels down. If you live above someone, a leak in your flat becomes their ceiling. Tell your managing agent early. We work in managed buildings across London and coordinate access between flats regularly.
What is the most common cause of hidden leaks?
Corroded compression joints, pinholes in copper pipe caused by aggressive water or poor installation, failed flexible hoses under sinks, and cracked waste connections behind baths. Flexible hoses are the most underrated. Check yours.
