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A leaking pipe is one of the few household faults that gets more expensive by the hour. Water runs along joists, soaks into screed and plasterboard, and often surfaces a metre or more from where it escaped. The US Environmental Protection Agency's WaterSense programme estimates that leaks in an average household can waste nearly 10,000 gallons (close to 38,000 litres) a year, before anyone counts the damage to floors, ceilings and the flat downstairs.
This page brings together what we cover on leaks: how they show themselves, the first hour, the checks you can run yourself, how specialists trace hidden leaks and what the repair usually involves.
How leaks give themselves away
Some leaks are obvious: a jet of water from a split pipe under the sink, or a puddle spreading from behind the washing machine. Most are slower and quieter, and show up through side effects rather than running water.
What you can see
- Brown or yellow rings on a ceiling, often with a slightly bubbled texture.
- Paint or wallpaper lifting low on a wall, or a tide mark creeping upwards.
- Grout that stays dark long after the shower has dried, or tiles that sound hollow when tapped.
- Laminate or wooden flooring that cups, swells at the joints or feels soft underfoot.
- Black mould returning to the same corner however often you clean it.
What you can hear, smell or read
A hiss or trickle inside a wall when every tap is shut deserves attention, especially at night. A musty smell in one cupboard often comes before any visible stain. Then there are the numbers: a water bill that jumps for no reason, or a combi boiler gauge that keeps falling, which points to a leak on the heating side rather than the mains. Our guide to the signs of a hidden water leak goes through each clue and what it usually means.
The first hour after you find a leak
When water is actively escaping, the order of what you do matters more than speed.
- Turn off the water at the stopcock. In houses it is usually under the kitchen sink or where the supply pipe comes up through the floor. In flats it may be in a riser cupboard, a corridor box or behind the bath panel. Turn it clockwise until it stops. If it is seized, don't force it; use the external valve near the boundary or in the building's meter room.
- Keep water and electricity apart. If water is near sockets, light fittings or the consumer unit, don't touch them. Switch off at the main switch only if you can reach it from a dry spot with dry hands; otherwise keep clear and have a qualified electrician check things before the power goes back on.
- Watch the ceiling. A bulging, sagging ceiling can come down without warning. Keep people and pets out of the room beneath it.
- Drain what is left in the pipes. Open the cold taps on the lowest floor and flush the toilets. If the leak is on the heating circuit, switch the boiler off too.
- Record everything. Photograph and film the leak, the damage and the meter reading before you start mopping up.
- Tell the people it affects: neighbours below, the landlord or building management, and your insurer.
Find your stopcock today, while nothing is leaking. Check that it turns, and tie a label on it so anyone in the house can find it in the dark.
Checks you can do yourself
The meter test
If you have a water meter, it is the best leak detector in the house. Turn off every tap and appliance, make sure no cistern or machine is filling, and note the reading. Leave everything off for at least half an hour, then read it again. If the numbers have moved, water is going somewhere. Many meters also have a small star or triangle that spins with even a tiny flow. Our step-by-step water meter leak test explains how to read different meter types and how to test the inside and outside of the property separately.
Narrowing it down
If the meter is moving, work through the usual suspects:
- Toilets. Put a few drops of food colouring in the cistern and wait twenty minutes without flushing. Colour in the pan means a leaking flush valve, a very common silent leak.
- Appliance valves. Close the isolation valves to the washing machine, dishwasher and fridge, then repeat the meter test.
- Under sinks and baths. Run a dry tissue along each joint; any dampness shows up straight away.
- The buried supply pipe. If the meter still moves with your internal stopcock closed, the leak is probably between the meter and the house.
How professionals find hidden leaks
When the simple checks point to a leak inside a wall, under a floor or below the garden, the next step is a leak detection survey. The aim is to pinpoint the source closely enough that the repair needs one small opening rather than a trench across the kitchen. Specialists usually combine two or three methods to confirm a location.
| Method | How it works | Best for | Limits |
|---|---|---|---|
| Acoustic listening | Ground microphones pick up the sound of water escaping under pressure | Supply pipes under floors and paths | Background noise; plastic pipe carries sound poorly |
| Thermal imaging | A camera shows temperature differences across a surface | Hot water and heating pipes | Cold-water leaks are harder to see |
| Tracer gas | The drained pipe is filled with a harmless hydrogen and nitrogen mix, detected where it escapes | Small leaks, plastic pipe, thick floors | The pipe must be emptied and isolated first |
| Pressure testing | An isolated section is pressurised while a gauge shows whether it holds | Confirming which circuit leaks; proving a repair | Shows which section, not the exact spot |
Moisture meters and inspection cameras fill in the picture. For more on the equipment and what a survey report should contain, read electronic leak detection explained.
Repair options once the leak is found
Remaking a joint
Many leaks come from joints rather than the pipe itself: a compression fitting with a tired olive, a soldered joint where the solder never flowed all the way round, or a push-fit connector on pipe that wasn't cut square. Once exposed, remaking the joint or swapping the fitting is often a short job.
Replacing a section
Where copper has pitted, plastic has been pierced by a nail or a pipe has split in a frost, the damaged length is cut out and a new piece joined in. A good plumber will look at the pipe either side, because one pinhole in old copper can mean others are coming.
Re-routing
When a leak is buried in a concrete floor or a tiled wall, digging it out is not always the best answer. Re-routing abandons the old run and puts new pipe along an accessible route, such as a ceiling void, a boxed-in corner or along a skirting. It often causes less disruption and makes future repairs easier.
Relining
Relining puts a new resin layer inside the existing pipe, which cures in place. It is common for drains and sometimes used on supply pipes. Suitability depends on the pipe's material, diameter and condition, and anything carrying drinking water must meet local rules on approved materials, so ask which product would be used.
Whatever the repair, the pipe should be pressure tested before the wall or floor is closed up. If you are comparing tradespeople, our guide on how to choose a plumber covers the questions worth asking.
Insurance and documentation
Policies differ between insurers and countries, so read your own wording. Broadly, many home policies cover damage caused by escaping water, and some also pay towards finding the leak, often called trace and access cover. The failed pipe or fitting itself is frequently excluded, and a leak that went unnoticed for months may be treated differently from a sudden burst.
To support a claim, report it promptly, keep the photos and meter readings from the first hour, hold on to the failed part, and ask for a written survey report and an itemised invoice. Don't throw away damaged belongings until the insurer agrees. Tenants should tell their landlord in writing straight away; who pays for what depends on the tenancy and local law.
Stopping it happening again
- Replace rubber washing machine and dishwasher hoses before they perish.
- Re-seal around baths and showers when the silicone cracks or blackens.
- Insulate pipes in lofts, garages and against outside walls before winter.
- Have very high mains pressure checked; a pressure-reducing valve takes strain off joints.
- Look under every sink and behind each toilet with a torch a couple of times a year.
- Read the meter on the same day each month, so an unexplained rise stands out.
Common questions
Can a hidden leak be found without breaking anything?
Usually it can be located without damage, but the repair still needs access to the pipe. A good survey keeps that to a tile or two, a section of floorboard or a small hole in plasterboard.
Is a slow drip worth fixing quickly?
Yes. A slow drip inside a wall can keep timber and plaster damp for months, and the mould and rot that follow cost far more than the leak.
What if the water is coming from the flat upstairs?
Keep clear of any wet electrical fittings, contact the neighbours and building management at once, and photograph the damage. If nobody answers and water keeps coming, the building's main valve may need closing, which is normally the building manager's job.
