Water back-billing claims for UK businesses in 2026: how to challenge a retroactive bill, even without an SLC 7A

What "back-billing" means in the water market

"Back-billing" in the non-household water market means a recalculated bill or invoice for water and sewerage services delivered in a period before the most recent normal billing window. It usually happens when a meter reading is corrected long after the fact, when a wholesaler issues a delayed primary-charge adjustment to a retailer, or when a previously unbilled SPID is "discovered" on a multi-site portfolio. Some back-bills go back two or three years; we have seen claims that purport to cover periods of five years or more.

Unlike domestic energy — where Ofgem's SLC 7A places a hard 12-month back-billing limit on suppliers — non-household water has historically had a softer regime. The protections exist; they are simply spread across the Ofwat Customer Protection Code of Practice (CPCoP), the open-market codes that govern wholesaler-retailer interactions, and ordinary contract law.

The good news for businesses: a properly constructed challenge wins more often than it loses. The bad news: most businesses don't construct one. They pay, or they argue informally and accept a partial credit. That asymmetry is what this post is designed to fix.

The CPCoP 24-month rule

Ofwat's Customer Protection Code of Practice for the non-household retail market — most recently restated in the January 2026 draft v2.4 — defines a "Back-bill" as a recalculated bill for water or services provided in the 24 months preceding the date of the bill. The relevant operative provision sits at section 9.3.1, which restricts retailers from issuing back-bills covering periods more than 24 months before the bill date.

That 24-month window is the first line of defence. If your business receives a bill in May 2026 that purports to charge for water consumed in March 2023, the part of the claim that pre-dates May 2024 is, on the face of it, outside the CPCoP back-billing window — unless one of the limited carve-outs applies (broadly: where the customer obstructed or prevented accurate billing, or where the customer failed to provide reasonable cooperation on meter access).

The CPCoP also requires retailers to offer micro-businesses — defined for water purposes broadly in line with the Ofwat micro-business definition — a reasonable repayment plan when a legitimate back-bill is issued, with repayment over a period of up to 24 months at the retailer's discretion. That carries forward an important practical point: even where a back-bill is partially valid, it should not be demanded as a single lump sum.

Why this is not the same as energy SLC 7A

Three differences between the water CPCoP regime and the energy SLC 7A regime matter when you're constructing a challenge:

1. The water rule is in a code, not a licence condition. SLC 7A is a Standard Licence Condition: breach by a supplier triggers Ofgem enforcement powers under the Gas Act 1986 / Electricity Act 1989 with up to 10% of turnover penalties. The CPCoP is a code that retailers are required to comply with as a condition of operating in the open water market. Ofwat enforcement on CPCoP breaches is robust but the route to penalties is different.
2. The water rule is 24 months, not 12. A larger window means the protection is, on its face, less generous than energy. But because the water market has fewer disputes per customer, the practical impact is broadly comparable.
3. The water rule is more carve-out-heavy. Customer obstruction, refused meter access and similar grounds leave more room for a retailer to argue that the back-billing restriction does not apply. Your challenge needs to address these head-on rather than relying on the rule alone.

The Limitation Act 1980 backstop

Where the CPCoP doesn't fully bar a claim — for example because the retailer asserts a carve-out — the Limitation Act 1980 sets the long-stop. Under section 5 of the Act, an action for a sum recoverable under a simple contract cannot be brought after six years from the date on which the cause of action accrued, in England and Wales. The equivalent period in Scotland under the Prescription and Limitation (Scotland) Act 1973 is generally five years.

For unbilled water charges, the cause of action typically accrues when the charge becomes payable under the contract — usually a fixed period after the bill date. In practice this means a retailer cannot pursue a contested claim through the courts for periods more than six years before the date of issue (E&W) or five years (Scotland). After that window, the debt is "statute-barred". The debt itself may still exist in some technical sense, but it is unenforceable through the court system.

Three operational points on the Limitation Act:

• Acknowledging the debt re-starts the clock. If your business writes to the retailer accepting that some amount is owed, that acknowledgement under section 29 of the Act may re-start the limitation period. Don't acknowledge in writing without first taking advice on the exact wording.
• Part-payment also re-starts the clock. Paying any portion of the disputed sum can have the same effect. Pay only the undisputed elements and itemise what you are paying.
• The Act does not extinguish the underlying obligation; it bars the remedy. A retailer that has lost its court remedy may still attempt to set off the debt against future credits. Watch for this in subsequent invoicing.

Recent enforcement: Clear Business Water

The most useful precedent in this space is Ofwat's March 2026 enforcement action against Clear Business Water Limited. Ofwat identified that the retailer's standard Terms and Conditions of Supply were not aligned with the CPCoP back-billing requirements, and that some non-household customers had been billed for periods exceeding the permitted 24-month timeframe. Clear Business Water has begun rectifying the breach and refunding affected customers.

What the case establishes for businesses challenging back-bills:

• Mismatch between contract terms and the CPCoP doesn't override the CPCoP. A retailer cannot rely on its own terms and conditions to sidestep section 9.3.1. Don't accept "but the contract allows it" as a defence to a back-bill outside the 24-month window.
• Refund pathways exist. Where a retailer is found to have billed outside the rule, refunds — not just credits against future bills — are the appropriate remedy.
• Ofwat is actively monitoring. Compliance scrutiny in the non-household market is at a higher water-mark than at any time since the market opened in April 2017.

Building a challenge: documentary evidence

A back-billing challenge is won or lost on documents. Pull the following before you draft any correspondence:

1. The disputed bill itself — every line, including any narrative explanation of the recalculation.
2. All bills for the back-billed period. If your retailer says "we under-billed you in 2023 and 2024", you need to see the originals to test that claim.
3. Meter reading history. Most retailers will provide this on request. If the back-bill is driven by a meter exchange or a "true-up" reading, the reading sequence is critical.
4. Your own consumption records — utility-management software exports, half-hourly equivalents (where applicable), and any evidence of works that would have changed consumption (closures, refurbishments, water-efficiency installations).
5. The contract — the version in force during the back-billed period, not the version current today.
6. Any communication you sent to the retailer about meter readings, access or billing queries during the back-billed period. This is the evidence that beats the "customer obstructed" carve-out.

If any of these are missing, request them in writing. The CPCoP and the wider open-market codes oblige retailers to provide reasonable information access on request, and a refusal to provide records is itself useful evidence in any later complaint to CCWater or Ofwat.

Wholesaler-to-retailer pass-through

One quirk of the open water market: a substantial portion of back-bills originate not with the retailer but with the regional wholesaler (Severn Trent, Thames, United Utilities and so on). The wholesaler reissues a primary-charge calculation, and the retailer passes it through. CPCoP section 9.3.3 requires retailers to pass on wholesaler refunds proportionately when a recalculation results in over-payment — but the symmetric pass-through of an under-payment is governed by the open-market codes, not by CPCoP itself.

Two practical implications:

• "It's the wholesaler's number, not ours" is not a complete answer. The retailer is your contractual counterparty. They are responsible for ensuring that what they bill you complies with the CPCoP, even when the underlying calculation is the wholesaler's.
• Wholesaler-driven back-bills are often time-limited at source. The Wholesale-Retail Code limits how far back a wholesaler can issue corrected primary-charge data to retailers. A retailer who tries to back-bill you for periods outside the wholesaler reissue window is on weak ground.

Letter of complaint: structure that works

A formal complaint letter that gets results follows a predictable structure:

1. Identify the disputed invoice — invoice number, date, total, the specific line items in dispute.
2. State the back-billing window the retailer is seeking to charge for — be precise to the day.
3. Cite CPCoP section 9.3.1 and explain why the claim falls outside the 24-month window.
4. Address each carve-out the retailer might rely on — meter access, customer cooperation, supplied information — with documentary references showing they don't apply to you.
5. Cite the Limitation Act 1980 (s.5) as a backstop for any portion of the claim more than six years old (E&W) or five years old (Scotland).
6. Set out what you want — usually: written withdrawal of the disputed portion of the invoice, written confirmation that no further action will be taken on those amounts, refund of any payments already made against the disputed portion within 14 days.
7. State your escalation route — that if no satisfactory response is received within the retailer's published complaints timetable (typically 8 weeks), you will refer the matter to the Consumer Council for Water (CCWater) and, if appropriate, raise a formal compliance concern with Ofwat.

Escalation: CCWater, Ofwat and beyond

If the retailer's first response is inadequate, the formal escalation ladder for non-household water customers runs:

1. Retailer's own complaints procedure. Two-stage in most retailers; allow it to run.
2. The Consumer Council for Water (CCWater). Free, statutory, will mediate between you and the retailer. CCWater handles non-household complaints across England and Wales. They cannot impose a binding decision but their pressure resolves a high proportion of disputes.
3. Ofwat — compliance reporting route. Where the dispute reveals a possible CPCoP breach, you can report it to Ofwat as a compliance concern even if your individual case is settled. This is what triggered the Clear Business Water enforcement.
4. Litigation or set-off resistance. If a retailer attempts to enforce a statute-barred or CPCoP-barred claim through the courts or by set-off, take legal advice before responding.

For Scottish non-household water — a separately structured market under Scottish Water and the Central Market Agency — the equivalent complaints body is Citizens Advice Scotland's Extra Help Unit, with the Scottish Water Industry Commission for Scotland (WICS) as the economic regulator.

What good looks like

A successful back-billing challenge usually closes on three documents:

• A credit note from the retailer cancelling the disputed portion of the invoice.
• A written confirmation that no further action will be pursued on the cancelled amounts.
• A refund of any disputed amounts already paid, settled to your nominated account within 14 days.

From the £18.4m in incorrect charges we have recovered for 12,400+ businesses and households served, water back-billing has been one of the highest-yield categories on a per-case basis — the disputes are usually clean, the regulatory framework is well-defined, and retailers tend to settle once a properly cited challenge lands. If you have received a back-bill you suspect is outside the CPCoP window, send us the disputed invoice and the immediately preceding three bills via the compliance casework page and we will tell you, plainly, whether you have a case. Initial review is free; we work on a transparent fee model with no contingent fees on regulator complaints. See also our glossary entries on back-billing, SPID and microbusiness.