High water bill but no visible leak: how to find where the water is going

The bill has arrived and it is far higher than the last one, yet nothing in the house is dripping. No wet floor, no stain, no puddle under the sink. A high water bill with no visible leak is one of the most common reasons people ring us, and the water is nearly always going somewhere you cannot see: into the ground, down a drain, or into a floor.

This article takes you through the checks in the order we would do them at your house. The meter test first, because it proves whether water is really leaving the system. Then the toilets, the supply pipe under the garden, and the heating. Finally, what detection work adds when the checks say there is a leak but do not say where, and how to ask your water company about the bill.

First, rule out the bill itself

Before you look for a leak, look at the bill. Check whether it is an actual reading or an estimate, because an estimated bill followed by an actual one can land a year of catch up in one go. Check whether a meter has recently been fitted. Check whether anything in the house changed: a new bathroom, more people, a hose left running through a dry spell.

If none of that explains it, read the meter yourself and compare it with the reading on the bill. A misread meter happens. If your own reading is close to the bill and the usage is still far above normal, the next step is the test that settles whether water is leaving the pipes without being used.

The meter test that proves a high water bill is a leak

Turn off every tap and appliance that uses water. Make sure the washing machine and dishwasher are not mid cycle, nobody flushes a toilet, and any outside tap is closed. Find the meter, usually in a chamber in the pavement or front garden, or sometimes under the kitchen sink. Lift the lid and photograph the dial, including the small red numbers or the spinning wheel.

Wait 20 minutes without using any water. Photograph the meter again. If the numbers have moved, or the small wheel is turning, water is passing through the meter while nothing is being used. That is a leak. If the meter is still, the water you are being billed for is being used by something in the house, and the search moves to the toilets and the appliances.

Now do the test again with the internal stop tap closed, usually under the kitchen sink. If the meter stops, the leak is inside the house. If it keeps moving with the stop tap shut, the leak is on the supply pipe between the meter and the house. That one extra step tells you which half of the system to look at, and it is the first thing we will ask when you ring.

• Everything off, photograph the meter, wait 20 minutes, photograph again
• Meter moved: water is leaving the system somewhere
• Repeat with the internal stop tap closed
• Still moving: the supply pipe outside. Stopped: inside the house

The toilets and the overflow

A toilet that leaks from the cistern into the pan is silent, invisible and runs all day. The fill valve fails to shut off fully, or the flush valve seal no longer seats, and a steady trickle runs down the back of the pan and away. Because the water goes straight to the drain, it never shows as damp. It only shows on the bill.

To check, dry the inside of the pan above the water line with tissue and wait a few minutes. If the tissue wets, or you can see a faint ripple on the surface, the cistern is leaking through. A few drops of food colouring in the cistern make it obvious, because the colour appears in the pan without a flush. Check every toilet in the house, not just the one you use most.

Look outside as well. An overflow pipe that drips from the wall near a toilet or the loft tank means a valve is not closing. A loft storage tank with a faulty ball valve can run to overflow for weeks. These are plumbing repairs, usually quick ones, and they do not need a detection visit.

The supply pipe under the garden

If the meter kept turning with the internal stop tap closed, the leak is on the pipe between the meter and the house. You are responsible for that pipe from the boundary onwards, which is why the water company's letter about high usage lands on you rather than on them. The pipe is buried, often decades old, and on older houses may still be lead or galvanised iron.

Look for the signs that water is reaching the surface: a patch of lawn that is greener or softer than the rest, a damp area on the drive that does not dry, moss along a joint in the paving, or a trickle at the kerb in dry weather. Listen at the internal stop tap with the house quiet: a faint hiss with everything off is the sound of water escaping under pressure.

Often there is nothing to see at all, because the ground drains the water away. This is the leak people mean when they say they have a burst pipe and a high water bill but no wet patch. Finding it means tracing the pipe route and listening along it with a ground microphone, which is detection work rather than plumbing.

The heating filling loop and the boiler

A leak on the central heating circuit does not usually show on the water meter, because the heating is a sealed system. The exception is when the boiler's filling loop has been left open, or an automatic filling valve has been fitted. Then every drop lost from a radiator pipe under the floor is replaced from the mains, and the meter records it.

If the boiler pressure gauge sits at a steady figure but you have never topped it up, check whether the filling loop is connected and the valves are open. If they are, close them and watch the pressure over a day. A gauge that now drops confirms the heating is leaking, and the water meter was only telling you the system was being refilled.

A dropping gauge with the loop closed is a heating leak, not a mains leak. The usual place is a pipe under a ground floor, where the water goes into the screed or under the boards and takes weeks to reach the skirting. That is found with the thermal camera and tracer gas, not the ground microphone.

Where a water meter keeps spinning with no leak to see

People often tell us the water meter is spinning but there is no leak. There is always a leak if the meter turns with everything off. What they mean is that it cannot be seen, and the list of hidden places is long. A cold pipe under a solid floor. A pipe in the wall behind a kitchen unit. A joint under a bath panel that drips onto the floor and dries before anyone looks.

Outside, think about an outside tap with a split pipe behind the wall, a garden irrigation line, or a pipe feeding a garage, outbuilding or stable. A water softener that regenerates too often uses water you never see. A hot water cylinder with a faulty expansion valve can discharge to a drain pipe outside, steadily, for months.

The quickest way to narrow this down is to isolate parts of the house one at a time. Close the stop valve to the outside tap, or to the cylinder, or to a bathroom, and repeat the meter test each time. When the meter stops, you have found the section. If every isolation point leaves the meter turning, the leak is on a pipe you cannot isolate, and that is where detection starts.

What leak detection adds

By this stage you know a leak exists and roughly which part of the system it is on. What you do not know is the point on the pipe. Guessing means lifting floors or digging the drive until the pipe turns up. A detection visit replaces that guess with one marked spot and a reason for it.

For a supply pipe, we trace the route and work along it with a ground microphone while the pipe is under pressure. The sound of the escape peaks over the hole. For a pipe inside the house, the thermal camera shows cold water spreading under a floor or inside a wall, and a moisture meter confirms the wet area. Tracer gas is used where the camera cannot see, with a detector following the gas to the break.

You get a written report with the location, the readings and photographs. The repair is then a small job in the right place, and the report is what your insurer and your water company will both want to see when you apply.

What about the bill you have already been sent

Once the leak is repaired, you may be able to have the excess charge reduced. The water companies in our area, including Anglian Water, Essex and Suffolk Water, Cambridge Water, Affinity Water and Thames Water, each run a leak allowance scheme for metered customers. In general terms you need to have the leak fixed, provide evidence of the repair and give meter readings, and schemes are usually limited to one claim in a set period.

The terms, amounts and time limits differ between companies and change over time, so check the current terms on your own company's website or ring them. Our separate guide to water leak allowances explains the process for each company. Keep the detection report and the repair invoice, because they are the evidence the application asks for.

Questions people ask