Unusually high water bill: how to find a hidden leak

Your meter can tell you in two hours.

The answer in 2 lines. First check the bill: is it based on a real meter reading or an estimate? If you are not on a meter, a leak does not change your bill. If you are, turn off every tap and appliance (but leave the stop tap open), note the meter reading and use no water for one to two hours, or overnight. If the numbers have moved, water is leaking after the meter. Check the toilets first: a leaking toilet is the most common hidden leak. If the leak is on the underground supply pipe, have it repaired quickly and ask your water company for a leak allowance: most give one for this kind of leak.

The first 3 steps

Look at your bill: does it say actual or estimated reading? Compare the reading on the bill with the one on your meter today.
Turn off every tap and every appliance that uses water (washing machine, dishwasher, garden hose, water softener), but leave the stop tap open. Photograph the meter with the time, use no water for one to two hours (or overnight), then read it again.
Keep the bill, the meter photos and any letters: you will need them to ask for a leak allowance or to complain.

Stop: danger

A wet wall, floor or ceiling near a socket, light or the consumer unit (fuse box): do not touch anything wet. Switch off at the consumer unit only if it is dry and you can reach it without standing in water; otherwise leave the room and call 999 if there is danger.
Hot water cylinder or boiler: just look at the overflow or discharge pipe outside. Do not take anything apart: the water can be scalding and the appliance is live.
Water bubbling up in the street or a growing puddle around the meter or outside stop tap: keep away and report it to your water company's 24-hour leak line. Someone hurt or unwell: 999, or 111 if it is not an emergency.

Where the leak hides: what to check

Toilets: water trickling into the pan, or a few drops of food colouring in the cistern turning the pan water coloured within 15 to 30 minutes without flushing. Often a job you can fix yourself (valve or flush seal).
Taps and flexible hoses under sinks and basins: drips, a damp cupboard base.
Overflow pipes outside the house (from the cold water tank in the loft or a toilet cistern): water dripping or running.
The supply pipe, the underground pipe from your boundary to your house: a damp patch or unusually green grass in the garden or drive, the meter moving with everything off and nothing visible inside. This needs a plumber.
Hot water and heating: a warm patch on the floor, a combi boiler losing pressure again and again. Call a Gas Safe registered engineer for anything on a gas boiler.

If the meter does not move during the test, there is probably no leak right now: think about real use (new person in the home, garden watering, a leak already fixed) and check that the reading on the bill matches your meter.

What you can do yourself, and where to stop

The food colouring test on every toilet, twice a year.
Isolate room by room: if you have small isolating valves under sinks and toilets, close them one by one and watch the meter.
Small visible leaks: a tap washer, a hose, a toilet flush valve, with the water turned off.
Read the meter weekly for a month after a repair to check your use has come back down.
Stop there: buried or hidden pipes, anything on the hot water cylinder or boiler, or a meter that keeps moving when you cannot find why. That is a job for a qualified plumber. You can find one on WaterSafe, the national register of approved plumbers: search by postcode and pick a business listed for the work you need.

What not to do

Digging up the drive or breaking into a wall to "have a look": first ask your water company, some offer a free or subsidised supply pipe repair or leak check.
Paying the high bill without checking the reading: an estimated bill can be corrected with a real reading.
Waiting months before repairing: most leak allowances require a prompt repair and only cover the period of the leak.

Who pays and who to tell (England)

Who owns which pipe: your water company is usually responsible for pipes up to your property boundary (and usually the meter); the supply pipe from the boundary into your home, and all the plumbing inside, are normally the owner's responsibility. If you rent, the landlord must repair water pipes, sinks, baths and toilets (Landlord and Tenant Act 1985, section 11): tell them in writing.
The leak allowance: water companies in England are not obliged by law to cancel the extra water, but most have a leak allowance policy in their code of practice. It usually covers a leak on the underground supply pipe that you repair quickly, often only once; leaks inside the home (toilets, taps, appliances) are usually not covered. The rules and the form are on your company's website, for example Thames Water or United Utilities. Ask the plumber for an invoice that states the date and place of the leak.
If you disagree: complain to your water company first. If you are not happy with the answer, the Consumer Council for Water (CCW) can take up your complaint for free (how it works: Citizens Advice — Complaining about your water company). After that, the independent Water Redress Scheme (WATRS) can decide: see Water UK — Resolving disputes.
Not on a meter? Your bill is fixed (usually based on your home's rateable value), so a hidden leak does not change it. But fix it anyway: it can damage the house.

In your city

Your water company's name and leak line are on your bill; if you are not sure, use the Water UK postcode finder.

London: Thames Water for most of the city (some outer areas are supplied by Affinity Water or SES Water: check your bill).
Birmingham: Severn Trent.
Manchester and Liverpool: United Utilities.
Leeds and Sheffield: Yorkshire Water.
Newcastle: Northumbrian Water.
Bristol: Bristol Water (part of South West Water) for supply, Wessex Water for sewerage.

In Wales most homes are supplied by Dŵr Cymru Welsh Water, with its own leak policy. In Scotland (Scottish Water) and Northern Ireland (NI Water), households are generally not charged by meter, so a hidden leak does not usually raise a household bill there.

Good to know

Read your meter on the same day each month: an unexplained jump is the first sign of a leak.
Find your stop tap now and check it turns: see our guide on turning off the water.
If you struggle to pay a high bill, ask your water company about payment plans and social tariffs before the debt builds up.

In Bristol, Daniel's bill is almost three times his usual one. One evening he turns everything off and photographs the meter; in the morning it has moved. The food colouring stays in the toilet cisterns. A WaterSafe plumber finds a split in the supply pipe under the drive. Daniel sends the invoice to his water company with its leak allowance form, and the extra water is taken off his bill.

A made-up story, for illustration.

The figures (latest published)

Water bills 2026/27: average household bills in England and Wales rose again in April 2026, by around £33 a year on average according to the figures announced by the industry in January 2026; the rise varies by company (MoneySavingExpert, January 2026). The 2027/28 figures are not yet published.
Leaking toilets: CCW and water companies have campaigned on "leaky loos" because a silently running toilet can waste hundreds of litres a day; the amount depends on the leak, so we do not quote a single figure.
We found no official national figure for hidden leaks in homes, so this guide does not quote one.

Useful numbers (England)

999: danger to life (water near live electrics you cannot isolate, a collapsing ceiling).
Your water company's 24-hour leak line: on your bill and its website.
0800 111 999: National Gas Emergency Service, if you smell gas.
CCW (Consumer Council for Water): free help with complaints about water bills once your water company has replied; the steps are explained by Citizens Advice.

Bobby

Sources, verification, confidence

Verified on 1 November 2026, for England. Confidence: high for the meter test, the split of responsibility for pipes and the complaint route (company, CCW, WATRS); medium for leak allowances, which differ from one water company to another (check your company's policy); medium for the 2026/27 bill rise, taken from press coverage of the industry announcement. The government announced in 2025 and 2026 a reform of water regulation (a new regulator replacing Ofwat and a water ombudsman); until it takes effect, the routes above apply. This guide describes common cases, not a diagnosis.