The short answer
The quickest test for a hidden leak is the water meter: turn off every tap and appliance, note the reading, wait an hour without using water and check again. If the numbers have moved, water is escaping somewhere. Damp patches, a sealed heating system that keeps losing pressure, the sound of running water and unexplained high bills are other common signs.
Common signs of a hidden leak
Hidden leaks often show up indirectly before you ever see water. Look out for:
- Damp patches or staining on ceilings, walls or floors.
- Peeling paint, bubbling plaster or lifting floorboards and tiles.
- A musty smell or mould appearing where there was none before.
- The sound of running or hissing water when nothing is on.
- A boiler that keeps losing pressure, pointing to a leak on the heating circuit.
- Water bills that rise with no change in how you use water.
The water meter test
If you have a water meter, this is the simplest check. Make sure nothing is using water — taps, toilets, washing machine, dishwasher and outside taps. Take a photo of the meter reading, wait at least an hour, then check again. Any movement means water is flowing somewhere.
To narrow it down, close the internal stopcock and repeat. If the meter still moves, the leak is likely on the supply pipe between the meter and your house. If it stops, the leak is inside the property.
Checks you can do yourself
Before calling anyone, a few easy checks can rule out the obvious causes:
- Toilets: a cistern that trickles into the pan can waste a lot of water. Listen for refilling when no one has flushed.
- Under sinks and baths: look for drips on waste pipes, flexible hoses and isolation valves.
- Appliances: check behind the washing machine and dishwasher for damp or split hoses.
- Radiators and valves: look for drips or crusty white deposits around valves.
- Loft tanks: check the cold water tank and overflow pipe if you have one.
What to do straight away
If water is coming through a ceiling or pooling, turn off the water at the stopcock — often under the kitchen sink. If water is near light fittings or sockets, turn off the electricity at the consumer unit. Move valuables, catch water in buckets and take photos for your insurer. Then call a plumber.
How professional leak detection works
When a leak is hidden under a floor or inside a wall, a plumber uses a combination of methods to find it without pulling the house apart. These can include pressure testing to isolate which pipe run is losing water, thermal imaging to spot the temperature difference of a leaking hot or heating pipe, moisture meters to map damp areas and acoustic listening to pick up the sound of escaping water.
Pinpointing the leak first means only a small section of floor or wall needs opening to make the repair, which keeps disruption and making good to a minimum.
After the leak is fixed
Once the pipe is repaired, the area needs time to dry before redecorating. Keep photos and any written findings from the plumber, as insurers often ask for evidence of the cause of the leak.
Preventing leaks in future
Knowing where your stopcock is and checking it turns freely is the single most useful step. Lag pipes in lofts and outside walls before winter, replace perished washing machine hoses, and have dripping taps or running toilets fixed promptly rather than living with them.
Frequently asked questions
How can I tell if I have a leak under the floor?
Warm spots on a solid floor, damp or lifting floor coverings, and a water meter that moves when nothing is running are strong signs of a leak under the floor.
Why does my boiler keep losing pressure?
The most common reason is a leak somewhere on the heating system — a radiator valve, a pipe joint or the boiler's pressure relief valve. It should be traced rather than topped up indefinitely.
Who is responsible for a leak on the supply pipe?
In general, homeowners are responsible for the supply pipe within their property boundary, while the water company looks after pipes in the street. Your water company can confirm for your address.
Can you find a leak without damaging my floor?
Leak detection aims to pinpoint the leak so only a small area has to be opened for the repair, rather than lifting whole floors.