A higher payment is not the same as higher consumption
Start by identifying which figure changed: the direct debit, the billed amount, the tariff or the meter consumption. A payment can rise because an account is catching up a balance, even if current daily use has not changed. A bill can cover a different number of days or replace estimated readings with actual ones. These possibilities should be checked alongside, not instead of, a possible leak.
Put the previous and current bills side by side. Record the start and end dates, opening and closing readings, whether each is actual or estimated, the units used and any balance carried forward. If a meter was changed, ask for the exchange readings and date. Do not compare two monthly payment amounts as though they were measurements of water passing through the property.
A public UKPersonalFinance account described a sharp direct-debit increase and a disputed explanation involving a replaced meter and delayed readings. The supplier's account was not independently verified and no final outcome was established. It is a useful reminder to check the account history before authorising invasive leak work solely because a payment figure looks alarming. A plumbing fault and a billing issue can also exist together.
Source: Public account: a payment increase linked to disputed meter history
Use a small comparison table in your own notes
Write one row for each reading period: start date, end date, opening reading, closing reading, measured volume and known occupancy changes. Keep the payment balance in a separate column or sheet. This prevents an account catch-up from being mistaken for current water use and makes an estimated-to-actual adjustment easier to discuss with the supplier.
For example, a lower daily volume after a toilet repair supports the observation that use changed; it does not establish exactly when the fault began or prove that every earlier charge arose from it. Likewise, unchanged current use does not settle whether an older bill used the correct meter exchange readings. Each conclusion needs the relevant period's evidence.
Mark gaps as unknown rather than filling them with an assumed normal household figure. If you were away, note the dates and any equipment left operating. A short, accurate record is more persuasive than a complicated calculation built on guessed readings. It also helps the plumber and billing adviser work on the parts of the question they can actually resolve.
Compare daily use over equivalent periods
Once the readings and units are understood, compare consumption per day. As a simple arithmetic example, 10 cubic metres over 20 days is 0.5 cubic metres per day, or 500 litres per day. Ten cubic metres over 40 days is half that daily rate. These are calculation examples, not a benchmark for what your household should use.
Use the bill's measured volume rather than the payment amount for this comparison. Note changes in occupancy, visitors, time away, garden use and appliances. A family staying for several weeks can change demand; so can a toilet that quietly runs between flushes. The purpose is to identify an unexplained change, not to prove a particular cause from an average alone.
If the supplier has detailed meter data, ask what interval it represents and whether gaps or estimated periods exist. A graph can be informative but still needs the meter and account context. Keep your own dated observations where possible. If the readings seem inconsistent with the bill, ask the supplier to explain the discrepancy before assuming your arithmetic is wrong or the meter is defective. A clear table of dates and readings makes both the billing enquiry and any plumbing investigation more specific.
Confirm that you are looking at the right meter
In a block or a shared meter cupboard, match the meter identifier to the account and ask the supplier or building manager for clarification if it is uncertain. Do not choose the nearest meter by location alone. Labels can be incomplete or unclear, and a consumption test on the wrong meter cannot explain your bill. Avoid touching seals or altering metering equipment.
If the meter is safely accessible, photograph the identifier and reading with the date. Record the units and decimal display rather than copying only the largest digits without understanding them. Ask the supplier for its instructions for that model if the display is unfamiliar. Do not enter a chamber or lift a heavy cover to obtain a reading.
Where the meter has recently been replaced, request the old closing reading, new opening reading and exchange date. Ask how these were used in the bill. If a shared supply is involved, establish what the meter serves before concluding that unexplained use belongs to your flat alone. This is primarily a supplier or management question. A plumber may help understand the pipe arrangement, but cannot correct an account allocation or billing record simply by repairing a fixture inside the property.
Check ordinary water use before assuming a hidden pipe leak
Make a list of equipment that may draw water without someone standing at a tap: toilets, washing machines, dishwashers, outside taps, irrigation and any treatment equipment. Include delayed appliance cycles and other residents' use. A test described as “everything off” is only meaningful if those sources were actually excluded for the observation period.
Listen for toilets refilling without being flushed and look for a continuing trickle into the pan after normal refill. Check accessible taps and appliance connections for visible leakage without dismantling them. Ask the household about any change in routine. A small visible symptom can be relevant to consumption, but do not estimate the lost volume solely by its appearance or sound.
If a fixture is faulty, arrange repair and retain the date and findings. Do not assume that fixing one obvious drip accounts for the entire bill increase. Compare subsequent readings and ask the supplier to review the account if the numbers remain unexplained. Equally, avoid opening floors before checking accessible fixtures. A staged approach starts with clear, low-disruption observations, then uses the results to decide whether a concealed-supply investigation is warranted. It does not declare the first plausible explanation to be the final answer.
Use a no-use observation carefully
Follow your supplier's meter-check instructions and choose a period when nobody will intentionally use water. Record the reading and time, then repeat after the agreed interval. Note any unavoidable use rather than pretending the test was perfect. If the meter records a change, that establishes measured flow through that meter during the interval; it does not identify the exact source.
If the reading does not change, you have not demonstrated an ongoing flow during that observation. You have not ruled out an intermittent toilet fault, a problem that occurs only during use or an earlier leak that has stopped. Keep the conclusion proportionate. If the supplier has already flagged unusual patterns, share your observation and ask how it fits with its data.
Do not operate unfamiliar external or shared valves as part of a self-directed experiment. If isolation testing is needed to distinguish internal plumbing from a supply route, have the arrangement understood first and use competent help where necessary. A valve that is stiff, unidentified or shared introduces another risk. The most useful record states exactly what was observed, what equipment was idle and what was not checked. That gives the plumber a reliable starting point instead of an overconfident claim that a hidden leak has been proved or excluded.
A leak allowance has supplier-specific conditions
Thames Water's current household page says a potentially eligible leak must be repaired within four weeks of identification or notification, and the allowance claimed within three months of repair. It asks for confirmation such as the plumber's details and invoice, or its own job reference. Approval is not automatic, and the supplier's current terms should be checked for your case.
Do not wait for another bill before asking about the process. Record the date the leak was first identified, the repair date and the evidence available. Ask whether there are separate steps to report the repair and apply for the allowance. If another company supplies your water or handles the relevant charges, use that company's procedure rather than assuming Thames Water's dates apply across Greater London.
An allowance for lost water is different from paying the plumber's invoice or compensating for damaged finishes. Keep those questions separate when speaking to the supplier or insurer. A contractor can document the defect and work, but cannot promise a credit. If a deadline may be difficult because access, parts or another party is delaying the repair, contact the supplier promptly and retain its response rather than assuming an exception will be granted later.
Source: Thames Water: current leak-allowance eligibility and evidence
Ask for repair evidence that answers the supplier’s questions
Tell the plumber before the job if you intend to request a leak allowance. Ask for an accurate description of where the leak was found, what was repaired and when. Where readings or photographs were taken, retain them. Do not ask the contractor to backdate discovery, estimate an unsupported duration or state that all abnormal consumption definitely came from one defect.
A useful report distinguishes a confirmed leak from an investigation that found no active escape. If the fault is intermittent, describe the evidence and limitations honestly. The supplier may need readings after repair to assess the change. Keep a dated log under ordinary household use rather than changing your routine so dramatically that the comparison becomes difficult to interpret.
If you carried out an authorised minor repair yourself, ask the supplier what evidence it will accept; do not assume a purchased part receipt is sufficient. If the supplier repaired its own asset, retain the job number. If a landlord arranged the repair but you hold the water account, request the relevant documentation without unnecessary personal information. The evidence should connect the identified fault to a real repair, while leaving the supplier to assess how the billing adjustment is calculated.
Tenant, landlord and account holder may have different tasks
The person receiving the bill may not own the defective pipework or be authorised to commission substantial work. If you rent, report the suspected leak promptly to the landlord or agent and explain any supplier deadline. Keep the water account enquiry moving as well. Waiting for one party to finish every task before contacting the other can create avoidable delay.
Ask who will arrange access, approve the repair and provide the invoice or report. If the issue involves a communal supply, include the managing agent. Do not assume that water appearing in your flat establishes ownership of the pipe. A plumber's findings can help identify what the installation serves, while the tenancy, lease and supplier boundaries may still need checking.
If costs or responsibility are disputed, seek appropriate housing or consumer advice. Keep the technical and billing records factual. Do not stop rent or cancel agreed payments solely on the basis of a forum suggestion. A leak investigation, a landlord repair request and an allowance application are separate processes with different decision-makers. Coordinating them is more effective than asking the plumber to determine account liability or asking the water company to resolve an internal tenancy dispute without the relevant evidence.
If the bill is still wrong, pursue the billing question explicitly
Write down the specific issue you want the supplier to resolve: a wrong meter identifier, unexplained exchange reading, estimated period, disputed consumption calculation or an allowance decision. Attach the relevant dates and readings. A general statement that the bill is too high may lead back to the same leak-check advice without addressing the account issue.
Ask for a written explanation of the calculation and the next stage of the supplier's complaints process if you disagree. Keep reference numbers and a brief chronology. If affordability is an immediate problem, discuss support and payment arrangements with the supplier while the dispute is investigated. Do not assume a pending complaint automatically pauses collection or changes payment terms; obtain confirmation.
If an allowance is approved, compare the revised bill with the decision and check what period was adjusted. The credit may not mean every outstanding balance disappears. If the calculation remains unclear, ask how normal use and leak-period use were assessed. Keep the repair evidence available, but avoid repeatedly booking plumbing visits when the remaining problem is clearly an account explanation. Conversely, if post-repair consumption is still unexplained, tell the plumber and supplier rather than treating a credit as proof that the physical problem has ended.
Choose the next step from the evidence you actually have
If the direct debit rose but current measured use is consistent with the account history, begin with the supplier's billing explanation. If the correct meter shows unexplained use and accessible fixtures do not account for it, discuss leak investigation. If a known running toilet or visible leak has been repaired, retain the evidence, monitor readings and ask the supplier about its allowance process.
For an active escape of water, prioritise safe containment and repair rather than waiting for a billing decision. For uncertainty about the meter or shared supply, establish that arrangement before interpreting a test. These routes can run in parallel when necessary, but each should have a clear question and responsible person.
When contacting AK, provide the dates, readings, known symptoms and supplier findings. The purpose is to decide what plumbing investigation is justified, not to guarantee that a leak exists or a bill will be refunded. Attendance and labour charges are on the pricing page; agree the diagnostic scope before work. The strongest outcome is a reconciled account and an understood, serviceable installation. A high bill should lead to evidence and a targeted response, not automatic excavation, an assumed faulty meter or a promised allowance that nobody has approved.