High Water Bill No Visible Leak

Reviewed by the DCI Leak Detection team · Last updated June 2026

Your bill has climbed, sometimes sharply, yet you've checked under the sinks, peered behind the toilet and found nothing dripping. It's a common and frustrating position. The good news is that "no visible leak" rarely means "no leak". It usually means the water is escaping somewhere you can't see it. Below we walk through why a water bill goes up, the hidden causes that catch most UK homeowners out, and how to pin down what is actually happening before you spend money on a fix.

First, is it a price rise or a leak?

Before you assume the worst, rule out the simplest explanation. Water became noticeably more expensive in 2025. The average household water and sewerage bill in England and Wales rose by around £123, or about 26%, to roughly £603 a year from April 2025, according to Water UK and the regulator Ofwat. In the South West the increase was steeper still: South West Water bills went up by about 28%, taking the average to roughly £1.87 a day.

So if your bill has crept up by a quarter or so and your usage looks normal, much of that may simply be the new tariff. If it has doubled or jumped suddenly without any change in your household, that's a different signal. Our guide on why a water bill suddenly doubles covers that spike pattern in detail. A genuine hidden leak tends to show up as usage that's well above what your home would normally get through.

The hidden causes of a high water bill

When the bill is high but nothing is visibly dripping, the cause is almost always one of these. They have one thing in common: the water disappears quietly, so it never grabs your attention the way a burst pipe would.

A silently leaking toilet

This is the most common hidden cause, and the sneakiest, because the water runs straight into the pan almost silently. A leaking toilet commonly wastes around 200 to 400 litres a day, and the water industry estimates one can add roughly £300 a year to a metered bill. WaterSafe and Severn Trent put the national scale at around 400 million litres lost from UK toilets every day, with an estimated 5% to 8% of toilets leaking at any time. A quick test: wipe the back of the pan dry, then watch for a faint trickle running down from the cistern, or drop a little food colouring in the cistern and see if it appears in the pan without flushing.

An underground supply pipe leak

The pipe carrying mains water from the boundary into your home runs underground, often beneath a drive, lawn or path. A crack or pinhole there can leak continuously and show no surface sign at all, especially on free-draining ground. This is a frequent cause of a stubbornly high bill with nothing visible inside the house, and it's the homeowner's pipe to sort out (more on that below). It's the kind of fault non-invasive underground water leak detection is built to pinpoint without digging up the whole garden.

Dripping taps and worn washers

A single dripping tap looks trivial, but it adds up: Water UK and WaterSafe estimate a dripping tap wastes around 5,500 litres a year. Check every tap, including the outside and utility ones, and any garden or appliance connections. A worn washer is cheap to replace and an easy early win.

A central heating system topping itself up

A leak on a heating circuit, whether under floors, behind radiators or on the boiler, can make the system lose pressure and quietly refill from the mains. If you're forever topping up the boiler pressure, that water is going somewhere. Our water leak detection service covers heating leaks as well as plumbing ones.

How to check your meter for a hidden leak

Your water meter is the most reliable home test for a hidden leak, and our guide on how to check your water meter for a leak walks through it step by step, and it costs nothing. Here's the method utility companies recommend:

1. Turn everything off. Close all taps and stop every water-using appliance: washing machine, dishwasher, ice maker, irrigation. Don't flush the toilet during the test.
2. Read the meter, or watch the flow indicator. Many meters have a small spinning dial or triangle that moves whenever water flows. With everything off, it should be completely still.
3. Wait and re-read. Note the reading, leave the water off for an hour or two with no one using any, then read again. If the figure has moved, water is escaping somewhere.
4. Isolate inside versus outside. Now turn off your internal stop tap (usually under the kitchen sink). If the meter stops, the leak is inside the house. If it keeps running, the leak is on the supply pipe between the meter and your home.

That last step is the useful one: it tells you whether you're hunting a fitting indoors or a buried pipe outside. As the next section explains, it also tells you who's responsible for it.

Who pays for an underground leak?

This catches a lot of people out. Your supply pipe, the section running from the boundary (or the external stop tap, if there is one) into your home, is the homeowner's responsibility to maintain. So a leak on that buried length is yours to find and repair, not the water company's. The company looks after the water main in the street and the communication pipe up to the boundary. This split is set out by Ofwat, the Consumer Council for Water and South West Water.

Because it's your pipe, finding the leak precisely matters: you want to fix one small section, not excavate the whole run. That's the case for proper detection rather than guesswork with a spade.

Can you claim some of the cost back?

Possibly. Most water companies, South West Water included, run a leak allowance scheme that can credit part of the extra cost once a leak has been found and repaired, recognising that the water never reached your taps. If you are with South West Water, our guide to South West Water's leak allowance explains who qualifies and how to apply. You'll generally need evidence that the repair has been done. If South West Water has already contacted you about unusually high usage, our guide on what to do when South West Water says you have a leak walks through your responsibilities and the steps to take. A clear detection report supports both the repair and any allowance claim, and if the damage is one you intend to claim on your home insurance (our guide explains whether a water leak is covered by insurance) it doubles as an insurer-ready trace and access report.

When to call a leak detection specialist

DIY checks will catch the obvious things: a running toilet, a dripping tap, a meter that won't sit still. But if the meter shows water moving with everything off and you can't see where it's going, the leak is hidden, and chasing it by lifting floors or digging at random does more harm than good.

That's where non-invasive detection earns its keep. Using thermal imaging, acoustic sensors and tracer gas, a specialist can pinpoint a hidden leak, whether under a floor, behind a wall or out on the supply pipe, with the least possible disruption, then give you a report you can use for the repair and any allowance claim. Across Cornwall and Devon, our water leak detection team does exactly that, every week.

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