Statutory Inspections · Mandatory · Pre-Construction

Section 104 Sewer Adoption Agreement Record

A record tracking Section 104 sewer adoption agreements with the sewerage undertaker from pre-application through to formal adoption. Covers design approval, agreement execution, bond details, construction inspections, CCTV survey, water testing, maintenance period, and formal adoption. Without S104 adoption, sewers remain private. Mortgage lenders require adopted sewers on residential developments.

Last reviewed: 2 April 2026 — This guide reflects UK law as of this date. Water Industry Act 1991 s.104 remains current with no amendments enacted as of 2 April 2026. Next scheduled review: 2 April 2027.

Legal basis	Water Industry Act 1991 Section 104
Record type	T14 Section 104 Sewer Adoption Agreement Record
Purpose	Sewers adopted as public sewers by the sewerage undertaker — without adoption, they remain private drains
Mortgage lenders	Most mortgage lenders require confirmation that foul and surface water sewers are adopted or will be adopted — private drains can affect property saleability
Bond	Developer provides a bond (typically 10% of construction cost) to the sewerage undertaker as security for completion of the works
Regulator	Ofwat (Water Services Regulation Authority)

1. What It Covers

A Section 104 sewer adoption agreement is the legal mechanism by which sewers and lateral drains constructed by a developer are adopted as public sewers by the sewerage undertaker (the local water and sewerage company). Without a Section 104 agreement, the sewers remain private drains — meaning the property owners served by those drains are collectively responsible for their maintenance, repair, and eventual replacement. This has significant implications for property purchasers and mortgage lenders.

Most mortgage lenders require confirmation that foul and surface water drainage serving a new development is either already adopted or subject to a Section 104 agreement that will lead to adoption. A development without adopted sewers can be difficult or impossible to sell. The Section 104 process involves pre-application discussions, design approval by the sewerage undertaker, execution of a formal agreement, the provision of a bond, construction to the approved design under the undertaker's inspection regime, completion testing, a maintenance period (typically 12 months), and finally formal adoption and bond release. The process is lengthy — from initial application to formal adoption can take two to three years or more.

Start S104 negotiations at RIBA Stage 3 — the process takes months

The Section 104 application and design approval process typically takes three to six months, and the sewerage undertaker will not execute the agreement until the design is fully approved. Construction of adoptable sewers must not commence until the agreement is executed. If the S104 process is not started until after planning consent is obtained, the drainage programme may delay the overall construction programme. Early engagement with the sewerage undertaker — ideally at RIBA Stage 3 — allows design issues to be resolved before they become programme-critical.

“A sewerage undertaker may...enter into an agreement with any person constructing or proposing to construct...a sewer or disposal main...for the adoption of the sewer or disposal main.”— Water Industry Act 1991 Section 104(1)

2. Key Content

The Section 104 adoption record should track every stage of the process from initial application through to formal adoption and bond release. The following table sets out the key areas to be recorded.

Area	Detail required
Project reference	Development name, site address, planning application reference, developer name and contact, number of plots or units served by the proposed adoptable sewers
Sewerage undertaker	Name of the sewerage undertaker (e.g. Thames Water, Severn Trent, United Utilities, Southern Water), S104 application reference number, contact details for the adoption team, assigned case officer
Sewers to be adopted	Schedule of all sewers and lateral drains proposed for adoption — foul, surface water, and combined. Lengths, diameters, materials, gradients, and manhole references. Marked up on the adoption plan drawing
Pre-application	Date of pre-application enquiry, sewerage undertaker's initial response, any pre-application design comments, capacity assessment outcome (is there capacity in the downstream public sewer network?), any requirement for off-site reinforcement
Design approval	Date of formal S104 application submission, design drawings and calculations submitted, sewerage undertaker's design review comments and amendments required, date of final design approval. Design must comply with Sewers for Adoption (or the Design and Construction Guidance published by Water UK)
Agreement execution	Date the S104 agreement is executed (signed by developer and sewerage undertaker), agreement reference number, parties to the agreement, plan attached to the agreement showing the sewers to be adopted, any special conditions
Bond	Bond type (cash deposit, insurance bond, or bank bond), bond amount (typically 10% of the estimated construction cost of the adoptable sewers), bond provider, bond reference, date bond lodged with the sewerage undertaker, bond renewal dates if applicable
Construction phase	Construction start date (must be after agreement execution), sewerage undertaker's inspection regime (stage inspections at key points — formation, bedding, jointing, backfill, manhole construction), inspection records and sign-offs, any non-conformances raised and corrective actions taken
Completion tests	CCTV survey of all adopted sewers (to WRc standards), air or water pressure testing of all pipes, manhole inspections, flow testing where required. Test results submitted to the sewerage undertaker for approval. Any defects identified and remediation completed
Maintenance period	Start date of the maintenance period (typically 12 months from the date the sewerage undertaker confirms satisfactory completion), developer's obligations during the maintenance period (repair any defects, maintain manholes, keep sewers operational), final inspection at the end of the maintenance period
Formal adoption	Date of formal adoption — the sewerage undertaker issues a vesting certificate or declaration confirming the sewers are now public sewers. From this date, the sewerage undertaker is responsible for maintenance and repair. Record the vesting certificate reference and date
Bond release	Date of bond release following formal adoption. The sewerage undertaker releases the bond once the sewers have been formally adopted and all obligations under the S104 agreement have been discharged. Confirm the bond has been returned or cancelled

3. Common Mistakes

Constructing adoptable sewers before the S104 agreement is executed

Sewers constructed before the S104 agreement is executed will not be inspected by the sewerage undertaker during construction and may not meet the required standards. The undertaker is likely to require retrospective CCTV survey and testing, and may refuse to adopt sewers that were not constructed under their inspection regime. In the worst case, the sewers may need to be reconstructed. The S104 agreement must be fully executed before any construction of adoptable sewers begins.

Not including S104 costs in the development appraisal

The costs associated with the S104 process are significant and include the application fee, design fees, the bond (typically 10% of adoptable sewer construction cost), inspection fees charged by the sewerage undertaker, CCTV survey and testing costs, and any off-site reinforcement works required. Developers who fail to include these costs in the development appraisal may face unexpected expenditure that affects project viability. The bond alone can represent a substantial cash commitment or insurance premium.

Failing to coordinate the S104 programme with the construction programme

The S104 design approval and agreement execution process typically takes three to six months. If the developer does not start the process early enough, the drainage works may be delayed, which in turn delays plot completions and sales. The S104 programme must be integrated with the overall construction programme, with the application submitted no later than RIBA Stage 3 to ensure the agreement is executed before drainage construction needs to begin.

Assuming all site drainage will be adopted

The sewerage undertaker will only adopt sewers that serve more than one property and that meet the design and construction standards. Private drainage serving a single property, SuDS features (which may be adopted by the local authority under Schedule 3 of the Flood and Water Management Act 2010), and highway drainage (adopted by the highway authority) are excluded from the S104 agreement. The developer must clearly identify which drains are proposed for S104 adoption and which are private or will be adopted under a different mechanism.

4. Frequently Asked Questions

What is the difference between Section 104 and Section 106?▾

Section 104 and Section 106 of the Water Industry Act 1991 serve different purposes. Section 104 provides for the adoption of new sewers constructed by a developer — the developer builds the sewer to the undertaker's standards and the undertaker adopts it as a public sewer. Section 106 provides for the connection of a new drain or sewer to an existing public sewer — it gives the developer a right to connect, subject to giving notice and complying with the undertaker's requirements for the connection. Most developments require both: a S106 connection to the existing public sewer network, and a S104 agreement for adoption of the new on-site sewers. They are separate applications and separate agreements.

Can a sewerage undertaker refuse to adopt sewers under S104?▾

A sewerage undertaker is not obliged to enter into a S104 agreement — Section 104 is permissive, not mandatory. However, in practice, sewerage undertakers will adopt sewers that meet their design and construction standards. Refusal is most likely where the proposed sewers do not comply with the design standards, where the developer has a history of poor-quality construction, or where the proposed sewers would create an unreasonable maintenance burden on the undertaker. If the undertaker refuses, the developer can escalate the matter to Ofwat, but this is rare.

What happens if the developer goes into administration before adoption?▾

If the developer enters administration before the sewers are formally adopted, the bond provides security for the sewerage undertaker to complete or remediate the works. The bond amount (typically 10% of adoptable sewer construction cost) is intended to cover the cost of bringing the sewers to adoptable standard. If the bond is insufficient, the undertaker may be left with sub-standard sewers that it is reluctant to adopt. In this scenario, the householders served by the unadopted sewers may be left with private drains until the situation is resolved — which can affect property values and mortgage availability.

How long does the entire S104 process take from start to finish?▾

The typical timeline from initial S104 application to formal adoption is two to three years. This breaks down approximately as follows: design approval and agreement execution (three to six months), construction (depends on the scale of the development, but typically six to eighteen months for the drainage element), completion testing and defect remediation (one to three months), maintenance period (twelve months), and formal adoption and bond release (one to three months). The process can take longer if design amendments are required, if construction defects are identified, or if the maintenance period reveals issues that need remediation.

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