The average UK hidden leak wastes 400 litres per day and, if left, causes damage that costs 20 times more than the fix. The good news: you can spot one without any equipment. Here is how.
Signs you probably have a hidden leak
- Water bill up over the last 3 months with no lifestyle change
- Damp patch on a wall, floor or ceiling with no obvious cause
- Boiler pressure keeps dropping (weekly top-up = leak on the system)
- Musty smell in a room or cupboard
- Mould growth in an unexpected spot
- Warm patch on the floor (hot water pipe leak under screed)
- Sound of running water when everything is turned off
The water meter test (do this first)
Find your water meter (usually outside near the boundary, or in a pit under a cover). Then:
- Turn off every tap, appliance and toilet cistern in the house
- Wait 5 minutes for the system to settle
- Note the meter reading
- Wait 60 minutes with no water used
- Read the meter again
If the reading has moved at all with nothing running, you have a leak. Even a tiny movement is significant over 24 hours.
Narrowing it down
Is it the boiler system?
Turn off the boiler and check pressure gauge. Note pressure. Wait 24 hours without heating on. If pressure has dropped, leak is on the central heating side (radiator joint, pipe under floorboards, TRV).
Is it the toilet?
Put food dye in the cistern. Do not flush. Wait 30 minutes. If dye appears in the bowl, the flush valve is leaking (very common, wastes 400 litres per day, easy fix).
Is it under the floor?
Warm patches on tiled floors, damp on downstairs walls at low level, or a musty cupboard usually = leak on the incoming main or a hot water pipe. Needs professional detection.
What professional leak detection costs
- Basic acoustic detection: £180
- Thermal imaging survey: £280
- Tracer gas leak detection (for concealed pipework): £380
- Full report suitable for insurance claim: £480
Most home insurance covers "trace and access" costs under buildings cover. Check your policy before booking.
Common leak points
- Old rubber washers on stopcocks
- Compression joints under sinks that have loosened over time
- Failed flush valve in toilet cistern
- Bath waste pipe on the wrong fall
- Radiator TRV valve seal
- Boiler PRV (pressure relief valve) discharging
- Hot water cylinder overflow (older systems)
What NOT to do
- Do not ignore it. Water damage compounds quickly.
- Do not accept "we cannot find it, so probably nothing" from a plumber. A real leak needs proper detection kit.
- Do not try to open floors or walls yourself to look for it. You risk making the damage worse.