If your latest water bill is dramatically higher than usual and you haven’t changed how much water you use, there’s a leak somewhere. In our experience, by the time the bill arrives the leak’s been running for weeks — sometimes months.
Here’s the test we use first, the six hidden causes we find most often, and how to know when it’s time to call a specialist.
01 The 30-minute meter test
This is the single fastest way to confirm whether you have a leak before calling anyone:
- Make sure every tap, appliance and toilet in the property is off
- Find your water meter (usually outside, at the boundary of your property, under a small lid in the pavement)
- Note the reading exactly — photograph it if it helps
- Wait 30 minutes without using any water in the house
- Read the meter again
If the number has changed, water is escaping somewhere. That’s a leak, full stop — visible or not.
If the meter is the kind with a small spinning dial (most newer meters), watch that dial during the 30 minutes — if it’s moving with everything off, you have a leak.
The six hidden causes we find most often
02 A leaking toilet flush
This is the most common cause we find — and the easiest one for homeowners to miss because it’s usually silent.
The flush valve at the bottom of the cistern wears out and lets a thin stream of water trickle into the bowl 24 hours a day. A single leaking toilet can waste over 200 litres of water per day — enough to add £20-£40 a month to your bill.
How to test
Put a few drops of food colouring in the cistern (not the bowl) and don’t flush for 30 minutes. If colour appears in the bowl, the flush valve is leaking. Replace the flapper — a five-minute job, parts cost £5-£15.
03 A dripping tap or shower
A tap dripping once every two seconds is roughly 12 litres per day — nearly 4,400 litres a year. Multiply that across two or three drippy taps and a slow-leaking shower and you’re into hundreds of pounds annually.
Almost all drips are a worn washer. Easy DIY fix or a quick plumber call-out.
04 A buried supply pipe leak
The supply pipe between your water meter at the boundary and where it enters your house is your responsibility to maintain. If it springs a leak underground, all of that water escapes into the soil before it ever reaches your taps — but the meter still records it as “used”.
Signs you might have a buried supply leak:
- A patch of garden, driveway or path that’s permanently damp or sinking
- Lower water pressure than usual at the tap
- The meter shows water use even with everything off
- A letter from your water company about a meter discrepancy
This is one of the most common reasons people call our PBD Leak Detection team — supply leaks are completely invisible from the surface, but acoustic and gas tracer detection can pinpoint them to within a foot before any digging starts.
05 A leak under floors or behind walls
Pinhole leaks in copper pipework or compression joint failures in older pipework often happen in places you can’t see — under floorboards, in wall cavities, in the loft. By the time damp shows up on the ceiling, the leak’s been there a while.
Catching these early avoids:
- Structural damage to joists and floorboards
- Mould growth in wall cavities (a health issue, not just a water issue)
- The insurance claim that follows when the ceiling comes down
06 A failing hot water cylinder
Older copper hot water cylinders eventually develop pinhole leaks at the seams. Water trickles out, the system tops itself up from the cold supply, and your meter keeps ticking — you never see a visible leak because the airing cupboard hides it all.
If you have an older immersion-style cylinder, take a torch to the airing cupboard and check for:
- Damp at the base of the cylinder
- Water stains on the wood below it
- Green or white salt-like deposits on the cylinder itself
07 An outside or garden tap left dripping
Easy to overlook. The garden tap that “sometimes drips a bit” can run several litres an hour 24/7. Either replace the washer or fit a quarter-turn valve that closes more reliably.
When to call a specialist
If you’ve done the meter test and confirmed there’s a leak — but you can’t find a visible cause and the toilet/taps test fine — the leak is hidden. That’s when leak detection earns its keep.
We use a combination of:
- Acoustic listening equipment — picks up the sound of water escaping through walls, floors and slabs
- Inert gas tracer detection — introduces a harmless gas into the pipework that escapes at the leak point and is detected at the surface
- Thermal imaging — reveals hidden moisture and temperature differentials in walls and ceilings
The detection visit gives you a written report with the exact leak location, so when the repair happens, only the precise area needs opening up — no tearing apart whole rooms.
Most UK water companies (including Thames Water) offer a leak allowance scheme: if you fix a hidden leak within a set time, they’ll knock part of the inflated bill off. Our written detection reports are accepted for these claims. We’re a WaterSafe Approved contractor — the UK national approved plumber scheme recognised by water companies across the country.