Leaks Other Plumbers Could Not Find

Most leak detection pages tell you which instruments the engineer carries. This one tells you what those instruments actually found. Out of our last 400 leak detection surveys, we located the cause in 95% of them. In 2% the water was coming from a neighbouring property. In 3% it was not plumbing at all: gutters, roofs and other structural defects letting water into the building.

That is the entire survey, remainder included, because a success rate you cannot see the failures of is not evidence of anything. The three numbers do different jobs. The 95% is why people call. The 3% is the one that decides whether an insurance claim survives. The 2% is the reason to believe the other two.

The last 400 surveys, split three ways

• 95%: cause found inside the property's own system. Supply pipework, waste runs, heating circuits, underfloor loops, cylinders, tanks, seals, and the joints nobody wants to lift a floor to reach. Found, isolated and repaired by the same engineer on the same visit.
• 2%: the water belonged to somebody else. Nearly always a flat above or alongside. The survey ends with a written finding that points at a neighbour's pipework rather than a bill for our repair.
• 3%: structural ingress. Blocked gutters, failed flat roof coverings, defective pointing, parapets, flashings and window details. Water entering from outside and behaving on the ceiling exactly like a burst pipe.

We publish that split because the people who ring us have usually already been told, confidently, that a leak was somewhere it was not. Non-invasive leak detection in London is a diagnostic trade before it is a plumbing one, and diagnosis has a hit rate whether or not anybody prints it.

What 70 litres an hour costs a London household

Some of the leaks we find are not dramatic. They are quiet, buried, and expensive. We regularly measure properties losing more than 70 litres an hour, continuously, into a floor slab or a garden. Nobody hears it. The first sign is the bill.

Here is that rate priced against Thames Water's published metered charges for 2026/27, which took effect on 1 April 2026: £2.7346 per cubic metre for clean water and £1.4721 per cubic metre for wastewater.

• 70 litres an hour is 1,680 litres a day, which is 613.2 cubic metres a year and roughly 153.3 cubic metres a quarter. Thames Water puts one cubic metre at about 25 quick showers, so the leak is running the equivalent of around 15,000 showers a year into the ground.
• Clean water alone: about £419 a quarter and £1,677 a year.
• Adding sewerage: household wastewater is billed on the same metered volume, so by default you are charged to treat water that went into your floor slab. That adds about £226 a quarter, taking the leak to roughly £645 a quarter and £2,580 a year.

Two honest caveats, and the second one is worth money to you. Fixed annual charges are excluded here, because you pay those whether you leak or not. And a hidden leak into a slab or a lawn never reaches the sewer at all, which matters: Thames Water says that if you can prove more than 10% of the water you use does not return to their sewers, you can apply to reduce the bill. That is an application you have to make, not an allowance that arrives on its own, so the real cost sits somewhere between about £419 and £645 a quarter depending on whether you claim it. Either end of that band is a holiday. Left running for a year, it is more than most people spend on their car.

The reason to state it that precisely is that a leak of this size is almost never fixed by waiting. It is fixed by measuring flow at the meter, isolating section by section, and putting an instrument on the one length of pipe that is actually losing water. If your bill has jumped and nobody has explained why, a Thames Water leak allowance only covers part of the damage, and only once the leak has been found and repaired.

Losing water now? Call 020 7123 8560. We answer 24 hours a day, every day of the year.

When three plumbing teams have already been and failed

A meaningful share of our work arrives after somebody else has given up. We are regularly called to properties where three separate teams of plumbers have attended, chased the damp patch, opened up a wall or a floor, found nothing, and left. By then the customer has paid three times for the privilege of a hole in their ceiling.

The reason is not that those plumbers were bad at plumbing. It is that finding a leak and fixing a leak are different skills with different equipment. A general plumber follows the visible evidence. Water does not respect the visible evidence: it tracks along a joist, crosses a room inside a floor void, and appears at the lowest point it can find, which is frequently nowhere near the failure.

What changes the outcome is method and sequence. Meter and flow analysis to prove there is a live loss and quantify it. Pressure testing to isolate which circuit is failing, so you are surveying one system instead of the whole building. Then acoustics, thermal imaging and moisture mapping to narrow the position, and tracer gas when the pipe is buried, under concrete or otherwise silent. Gas is the method that most often means nothing has to be opened up speculatively, which is exactly why we do not charge a premium hourly rate for it; the only addition is £80 for the bottle on the jobs that need one.

None of that is magic. It is the difference between a specialist and a generalist, which we have written about at length in leak detection specialist versus plumber. It is also why we work under no find, no fee: if we attend a confirmed live leak and cannot locate it, the detection time is not charged.

The 3% that is not escape of water, and why it decides your claim

This is the finding almost nobody in the trade will put in writing, and it is commercially the most important paragraph on this page.

Home insurance covers escape of water, which means water escaping from a pipe, tank or appliance inside the property. It does not mean water arriving from outside through the building fabric. Blocked gutters overflowing down a wall, a failed flat roof, cracked render, a defective parapet: none of those are escape of water. They are maintenance, or in some policies storm damage, and the underwriting is completely different.

So if a claim is submitted as escape of water and the cause is actually a blocked gutter, the claim is refused, and refused correctly. The homeowner has by then often spent weeks on it, may have had trace and access work authorised on a false premise, and has a declined claim on their record.

In 3% of our last 400 surveys, the cause was structural ingress rather than plumbing. Several of those were simply blocked gutters putting water into the house. We tell people that on the day, in writing, before anything is submitted.

How we tell the difference

The distinction is rarely a judgement call once the right tests are run:

• The meter test. Isolate the property at the stopcock and watch the meter. If the loss stops, the water is yours. If the meter is static while the ceiling is still wetting, it is not coming from a pipe under pressure.
• Weather correlation. Plumbing leaks are indifferent to the forecast. Ingress is not. A stain that darkens two hours into heavy rain and dries in a settled week is telling you where to look.
• Position and pattern. Ingress tends to track down external walls, at parapets, around chimney breasts, at window heads and below flat roof upstands. Pressurised leaks appear at joints, tees and penetrations.
• Water chemistry and temperature. Heating circuit water is treated and often warm, and thermal imaging separates a hot feed from a cold rainwater track quickly.
• Moisture mapping over time. Reading the same points across a visit shows whether the material is wetting, holding or drying, which distinguishes a live leak from historic ingress that has already stopped.

Getting this right first is what protects the claim. A survey that correctly identifies structural ingress lets you fix the actual defect for the price of gutter clearance or roof work instead of paying for exploratory plumbing and then losing the claim anyway. If insurance is involved, read our guide to insurance leak claims before you submit anything.

The 2% we could quietly have left out

In 2% of those 400 surveys, the leak was not the client's at all. It was coming from a neighbouring property, typically the flat above or the one sharing a party wall.

We could have folded those into the 95% and reported 97%. We do not, for the same reason we publish the 3%: the split is only useful if it is complete. And practically, a survey that ends with "this is not your pipework, here is where it is" is a good outcome. It stops you paying for repairs to a system that is sound, and it gives you a technical finding to hand to a neighbour, a landlord or a managing agent. Who then pays is a separate question, covered in water leak in a flat, who pays.

What you pay, and what that covers

Our leak work runs at £160 an hour, and that single rate covers finding the leak, isolating it and repairing it, with the same engineer on the same visit. Parts and materials are costed on top and agreed with you before anything is fitted. The rate does not change when tracer gas is needed; the only addition is £80 for the gas bottle.

• No find, no fee. Attend a confirmed live leak and fail to locate it, and the detection time is not charged.
• Heating and trace and access work is £200 an hour, and mains and supply pipe work is £180 an hour. Moisture mapping starts at £175. Emergency attendance is £220 an hour.
• Making good afterwards. We have handymen and builders in house to repair the water damage and put the room back as it looked, so you are not sourcing a second and third trade after the plumbing is done.
• Block managers, managing agents and estate agencies: no call-out fee on an ongoing arrangement, and the hourly rate reduces with volume.

Full detail is on our pricing page, and the guarantee itself is explained in no find, no fee leak detection explained.

Round the clock, London out to the M25

We operate 24 hours a day, seven days a week, across all 32 London boroughs and the City of London, out to the M25. A leak losing 70 litres an hour does not wait for Monday, and neither does the bill it is generating.

If you have a stain that keeps coming back, a bill that has jumped without explanation, or a plumber who has already been out and found nothing, call 020 7123 8560.