In This Guide
What is the Thames Water leak allowance?
The Thames Water leak allowance is a rebate on the water charges you were billed for while a leak was running on your property. Thames Water compares your usage during the leak against your usage during a comparable period without one, and credits the difference back to your account.
It only covers water lost to the leak. It does not cover the cost of the detection work, the excavation, the repair itself, or any reinstatement. Those sit with the homeowner. The allowance exists because a hidden leak is often invisible until a bill or a letter arrives, the water loss is involuntary, and charging the full amount would discourage people from repairing leaks quickly. Fast repairs help Thames Water hit their own leakage reduction targets, so the incentive works both ways.
The allowance is not automatic. It is a discretionary credit that Thames Water reviews on a case by case basis against published eligibility rules, and it can be refused if those rules are not met.
Who is eligible for the Thames Water leak allowance?
Eligibility is set by Thames Water and applies across their supply area. The rules are:
Requirement | Detail |
Metered customer | You must be on a Thames Water water meter. Unmetered customers on rateable value cannot claim, because the allowance is a rebate against metered usage |
Repair within four weeks | The leak must be repaired within four weeks of it being found. Leaving it longer disqualifies the claim |
Claim within 90 days | The claim form must be submitted within 90 days of the repair date, even if you have not yet received the bill covering the leak |
Proof of repair | A plumber’s invoice, a repair job reference, or insurance documentation confirming the leak was fixed and when |
Not caused by negligence | Not eligible if the leak was caused by negligence, or if you knew, or should have known, about the leak and failed to repair it |
Not under Section 75 | Not eligible if Thames Water repaired the leak under a Section 75 waste of water enforcement notice |
Maximum backdating | The allowance covers the period the leak occurred, to a maximum of two years, unless the leak was on Thames Water’s own pipework |
There are also rules on how many times you can claim. One claim per leak inside the property, but multiple claims allowed for separate leaks on the external supply pipe. The full detail is in Thames Water’s leakage code of practice.
The negligence exclusion catches more people than expected. A running toilet cistern, a dripping tap you knew about, or an obvious leaking joint you had been meaning to fix are all situations Thames Water can decline the claim on. The allowance is aimed at leaks you genuinely could not have known about, like a supply pipe failing underground.
How much is the Thames Water leak allowance worth?
Thames Water calculates the allowance by comparing your actual usage during the leak period against your usage during a comparable period without one, and crediting the difference at your metered rate. There is no fixed sum. The size of the allowance depends entirely on how much water you lost.
On a typical supply pipe leak that ran for a few months at a modest rate, the credit can be several hundred pounds. On a significant leak that ran for longer, it can be into four figures. The two-year cap applies where the leak took a long time to be identified.
For unmetered customers whose usage is not recorded, the allowance is based on typical use for a comparable household, but this only applies in specific circumstances since the standard rule is metered customers only.
Any bill increase since the leak was found still needs to be paid while the claim is reviewed. Thames Water asks you to keep paying as normal and issues the credit against the account once approved.
How to apply for the Thames Water leak allowance
The application is a form Thames Water publishes on their website, submitted after the repair is complete.
You will need your Thames Water account number, meter readings taken 14 days apart to confirm the leak has stopped, the date the leak was found, the date it was repaired, and proof of the repair. If a plumber carried out the work, that means their invoice or job reference. If it was covered by insurance, the insurer’s documentation. If Thames Water fixed a leak on their own pipework, their job number.
The form itself is downloadable from the Thames Water leak allowance page or you can request it by calling their team. Once submitted, Thames Water reviews it and, if approved, credits your account and sends an adjusted bill.
The 14-day meter reading gap matters. Thames Water uses those two readings to confirm the leak has actually stopped, not just to calculate the allowance. If the meter is still moving with all water use stopped, the leak is not fully repaired and the claim will not be processed until it is.
What a Thames Water excessive usage letter means
If a letter from Thames Water arrived before you knew anything was wrong, that letter is often the first sign of the leak the allowance is designed for.
Thames Water monitors meter data across its supply area. When a property’s consumption over a billing period is well above the average for its size and type, an automated alert generates the letter. For a typical London household, average daily consumption is around 310 litres. A property running at 700 litres per day or more is likely to trigger a flag.
The letter is not a fine or a demand for payment. It is a notification that consumption looks abnormal, and an invitation to investigate before the problem gets worse. Thames Water is telling you what their data shows, not diagnosing the cause. The investigation and any repair are your responsibility if the issue is on your supply pipe or inside the property.
The most common reason the letter arrives without any visible problem in the house is an underground leak on the supply pipe between the street and the property. That pipe is under mains pressure all the time, and a failure at a joint, a corrosion point or where it enters the foundations can let water escape continuously into the surrounding soil with no sign inside the building. That is exactly the situation the leak allowance was designed for.
What to do if you received an excessive usage letter
The order to work through is the same regardless of whether a letter arrived or a bill spiked, and it saves you both time and unnecessary excavation cost.
First, rule out internal causes. A running toilet cistern is the single most common domestic cause of a big usage increase, and it can waste 200 to 400 litres per day without being obvious. Add food colouring to the cistern and check the bowl half an hour later for colour bleeding through. Also check every tap, the outside tap, the appliance fill hoses on the washing machine and dishwasher, and any drip irrigation. If the meter covers more than one supply, check them all.
Second, carry out the 30-minute water meter test. Turn off every tap and appliance in the property. Read the external water meter and photograph the dial. Wait 30 minutes without using any water. Read the meter again. If it has moved, there is an active leak on the supply pipe. Our guide to how to check for a water leak at home sets out the meter test in full.
Third, check who is responsible for which section. The boundary is the external stop tap, typically located at or near your property boundary. Thames Water is responsible for the water main in the street and the pipework up to that stop tap. From the external stop tap into the property, including the underground supply pipe, is the homeowner.
Fourth, check your buildings insurance for trace and access cover before assuming you face the full detection and access cost. Most UK buildings policies include it and it typically pays for locating and reaching a hidden leak. That is separate from the Thames Water allowance, which covers the water charges. On many claims both apply: insurance for the finding and access work, Thames Water for the lost water.
Fifth, book the underground leak detection investigation. Digging speculatively is expensive and unreliable, because water escaping underground follows the path of least resistance and often surfaces well away from the actual failure.
Sixth, once the leak is repaired, apply for the leak allowance within 90 days.
How 0800 Homefix handles a Thames Water letter response
0800 Homefix locates underground supply pipe leaks across London using acoustic listening equipment and tracer gas detection. Acoustic detection narrows down the area of the failure, and tracer gas, a safe mixture of nitrogen and hydrogen introduced into the isolated pipe, rises to the surface at the failure point where a handheld hydrogen detector picks it up to within centimetres. The failure point is confirmed before any excavation is recommended.
Every underground leak investigation includes a written report documenting the detection methods used, the confirmed failure location with measurements from property reference points, and the repair recommendation. That report serves two purposes: satisfying insurer requirements for a trace and access claim, and providing the proof of repair Thames Water needs for the leak allowance application.
We charge the first hour’s labour in advance, with any further investigation or repair work quoted and agreed with you before it begins. Current rates are on our rates page. Our labour is guaranteed for 12 months, and any manufacturer part we fit carries the manufacturer’s own 12-month guarantee. We cover London and the South East seven days a week, 365 days a year. You can read more on our underground water leak detection service page.
Helpful resources
Thames Water’s own guidance is on the leaks at home and leak allowance pages. WaterSafe maintains the national register of approved plumbers for water supply pipe work.
Frequently Asked Questions
What is the Thames Water leak allowance?
It is a rebate on the water charges you paid while a leak was running on your property. Thames Water compares your usage during the leak against a comparable normal period, and credits the difference back to your account. It covers water lost only, not the cost of finding or repairing the leak.
How do I claim the Thames Water leak allowance?
Complete the leak allowance form on the Thames Water website after the repair is done. You need your account number, two meter readings taken 14 days apart to confirm the leak has stopped, the date the leak was found, the date it was repaired, and proof of repair (usually a plumber’s invoice). Submit within 90 days of the repair.
How long does the Thames Water leak allowance take to process?
There is no fixed timescale published, but Thames Water asks you to keep paying your bill as normal while they review the claim. If approved, the credit is applied to your account and an adjusted bill is issued. Straightforward, well-documented claims are typically processed within a few weeks.
Do I qualify for a Thames Water leak allowance for a running toilet?
Usually no. A running toilet is a visible, audible leak, and the negligence exclusion means Thames Water can decline the claim if you knew or should have known about it. The allowance is aimed at leaks that could not reasonably have been spotted without a meter test, most commonly underground supply pipe leaks.
Do I have to pay the bill while the leak allowance is being reviewed?
Yes. Thames Water asks you to keep paying as normal while they review the claim, to avoid the account falling into arrears. If the allowance is approved, the credit is applied to your account and adjusts the next bill.
Why has Thames Water sent me a letter about high usage?
Thames Water sends excessive usage letters when meter data shows a property consuming significantly more than the average for its size and type. It is not a fine or a demand. It is a prompt to investigate. If you cannot find a cause inside the property, an underground leak on the supply pipe is the most common explanation.
Can I claim the leak allowance more than once?
Yes for external supply pipe leaks, no for internal ones. Thames Water allows multiple claims for separate leaks on the external supply pipe, since these can recur, but only one claim for leaks inside the property.
Does trace and access insurance also apply?
Yes, and the two are separate. Most UK buildings insurance policies include trace and access cover, which pays for locating and reaching a hidden leak. The Thames Water allowance covers the lost water. On many claims both apply and are worth pursuing together.
Received a Thames Water Letter?
If you have received an excessive usage letter or your bill has increased sharply, the sooner the leak is located the smaller the eventual cost. 0800 Homefix locates underground supply pipe leaks across London with a written report your insurer and Thames Water can both use, seven days a week. Book online or through our underground leak detection page to arrange an inspection.
Editorial note: This article is general information about Thames Water’s leak allowance and excessive usage letter process. Eligibility rules and application procedures can change, so always check the current details on the Thames Water website or speak to their team directly.
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Editorial note: This article is intended as a general homeowner guide. All plumbing work on supply pipes should be carried out by a qualified, WaterSafe-registered plumber. If you suspect a gas leak, leave the property immediately and call the National Gas Emergency Service on 0800 111 999.
