Why has my shop's water bill doubled? Telling a leak from a tariff change or a meter fault

The quarterly bill arrives and it is twice what it was, and someone in head office wants an explanation by Friday. Before you pay it, dispute it or ring a plumber, work out which of three things has happened: more water really went through the meter, the bill is built on the wrong reading, or the charges themselves changed. Each has a different fix. The checks below take less than an hour between them, and most need nothing more than a torch and the last two years of bills.

Start with the bill itself

Put this bill next to the same period last year and go through it line by line.

Actual or estimated reads. A run of estimated bills followed by an actual read can land as one large catch-up charge. MOSL’s market guidance points to Ofwat’s customer protection code: where there is a water meter, customers must get at least one accurate bill a year based on an actual reading.
The meter serial number. Your bill shows the meter’s serial number and location. Check that number against the meter outside. Where several meters share one chamber, make sure you are reading your own.
The volume. Compare cubic metres before you compare pounds. If the volume is flat and the bill has jumped, the charges changed. If the volume has jumped, the water went somewhere.
How you are charged. GOV.UK explains that a business with a meter pays for the water it uses plus a set charge, and one without pays a set amount, usually based on the value of the property. You also pay for the drainage of water and effluent from the premises. A switch from one basis to the other shows up as a very different bill.

What the bill shows	Likely cause	Next step
Volume up, based on actual reads	A leak, or genuine extra use	Do the meter test below
Estimates, then one big actual read	A catch-up after estimated bills	Ask your retailer to recalculate on actual reads
Volume flat, charges up	A tariff or charge change	Ask your retailer to explain each change
Serial number does not match your meter	Billing on the wrong meter	Report it with a dated photo of your meter
Volume up, no leak found, use unchanged	A possible meter fault	Ask your retailer to arrange a meter check

Rule out genuine extra use

Leaks get the blame for plenty of bills that were really a change in how the shop runs. Think back over the billing period. A new ice machine, coffee machine or water-fed chiller all draw water every day. So does a new cleaning contract, a refit that added toilets, or a hot spell with more hand-washing. Builders on site count too. Write down anything that changed and roughly when; your retailer will ask.

Do the meter test

Welsh Water publishes a simple test for business premises, and it works on almost any metered supply:

Find your water meter. It is usually in the footpath outside your premises, and its location and serial number are on your bill.
Turn off everything that uses water, including ice machines, coffee machines, automatic urinal flushes and dishwashers. Read the meter, wait without using any water, and read it again.
If the dials are still moving, you probably have a leak. Find your internal stop tap, which is normally where the water enters the building, and close it by turning it clockwise.
Read the meter again. If the dials are still moving, the leak may be on the pipe between the meter and the stop tap. If they have stopped, the leak may be on your internal pipework or fittings.

Other signs Welsh Water lists include a big drop in water pressure, a hissing noise near the internal stop tap, damp patches or unusually lush growth on the ground, and an unexplained change on the bill. Photograph both meter readings with the time showing. Those two numbers help the engineer, your retailer and your insurer.

Who owns the pipe that is leaking

The water company usually owns the pipes up to the street boundary. Welsh Water describes the pipe between the boundary and your internal stop tap as your private supply pipe, and says that pipe and all the internal pipework are the owner’s responsibility to repair. The industry’s leak allowance guidance agrees on the split and adds that if you rent, your landlord is probably responsible for the pipework, which you should check with them.

It also matters who pays for the lost water. Welsh Water says that if the leak is your responsibility, you are usually liable for all the water charges it has caused. In England’s business water market, MOSL’s leak allowance guidance says supply pipe leaks should be repaired within 30 days of you becoming aware of them. If the wholesaler issues a leakage notice under Section 75 of the Water Industry Act 1991, it can require the repair within 14 days, and may repair it and recharge you if the deadline is missed.

If it is a leak: fix it, then claim the allowance

In the business water market in England, a leak on your pipework can qualify for a leak allowance from the wholesaler, claimed through your retailer. The conditions in the customer guidance include:

the retailer must apply within six months of the repair being completed
you need proof of repair, such as the invoice, and at least two actual reads at least two weeks apart after the repair, showing consumption back to normal
only one allowance is granted in any 24 month period
extra use from leaking internal fixtures and fittings does not qualify

Policies differ between wholesalers, and some reduce only the sewerage charge. For a leak you cannot see, usually underground or under the floor slab, a survey finds it before anyone digs. See water mains leak detection.

If it looks like the meter

Business meters in the English market are installed and owned by the wholesaler. MOSL explains that if a meter is faulty or cannot be found, your retailer can ask the wholesaler for a site visit. So your first call is to the retailer, with your meter test results, the photos and the serial number check.

If it is the charges

Ask your retailer to explain every line that changed. GOV.UK says that in England and Wales you can check with Ofwat whether you are able to choose your own supplier, and in Scotland you choose from the Water Industry Commission’s list of suppliers. Larger users may be eligible for a large user tariff.

If your retailer cannot sort it out, CCW gives impartial advice to business customers in England and Wales once you have tried to resolve the complaint with the retailer directly. Billing problems are common. CCW reported that in 2025/26 billing made up 90% of the business complaints escalated to it, and measured billing accounted for 54% of those billing cases.

What to have ready before you ring anyone

the last two years of bills
a dated photo of the meter showing the reading and serial number
your meter test results, with times
a list of anything that changed in how the shop uses water
the lease clauses covering pipework and repairs, if you rent

If the meter test points to a leak, call 0333 567 2615 to book a survey. Our engineers cover England, Scotland and Wales, and we aim to find and repair on the same day wherever the job allows.

Frequently asked

Can we get money back for water lost through a leak?

Possibly. In the business water market in England, a leak on your side of the meter can qualify for a leak allowance from the wholesaler, applied for through your retailer within six months of the repair. You will need proof of the repair and at least two actual meter reads, taken at least two weeks apart, showing your use is back to normal.

Our bills have been estimated for months. What should we do?

Take a dated photo of the meter showing the reading and the serial number, send it to your retailer and ask for the bill to be recalculated on that actual read. In England, where there is a meter, customers should get at least one bill a year based on an actual reading.

Who fixes the pipe between the meter and our building?

Usually whoever is responsible for the premises. Welsh Water describes the pipe between the street boundary and your internal stop tap as your private supply pipe. If you rent, the industry's customer guidance says your landlord is probably responsible for the pipework, so check your lease and ask them.