Guide
Adopt new sewers under Section 104
How to get new sewers adopted by the water and sewerage company under Section 104 of the Water Industry Act 1991. Covers the adoption agreement process, Design and Construction Guidance standards, bond requirements, the inspection regime, vesting of assets, and the separate Section 106 right to connect.
When this applies to your development
If you are building a residential or mixed-use development with two or more properties that will connect to a new sewer system, you will almost certainly need a Section 104 adoption agreement with the local water and sewerage company. This agreement commits the water company to adopt (take ownership of) the sewers and lateral drains you construct, provided they meet the required design and construction standards.
Without a Section 104 agreement, the sewers remain privately owned. That means you or a management company bear permanent responsibility for maintenance, repair, and any environmental liabilities. Mortgage lenders and house buyers expect adopted sewers, so failing to secure adoption can make properties difficult to sell.
Section 104 applies in England and Wales. Scotland has a separate regime under Scottish Water, and Northern Ireland operates under different legislation. This guide covers the position in England and Wales only.
Start the adoption process early. You should approach the water company before you begin constructing drainage infrastructure, ideally at the planning stage. Late applications cause delays, redesign costs, and potential enforcement issues.
What the agreement covers
A Section 104 agreement is a legally binding contract between you and the water and sewerage company. It sets out the terms under which the company will adopt the sewers, lateral drains, and sewage disposal works you construct. The agreement specifies the design standard, inspection arrangements, financial security, and the process for transferring ownership (known as vesting).
The agreement covers foul sewers, surface water sewers (where the water company accepts them), lateral drains, and associated infrastructure such as pumping stations. It does not cover private drains within individual property curtilages, which fall under Approved Document H.
How to apply for a Section 104 agreement
The adoption process has several stages. Allow sufficient time for each stage, particularly design approval, which can take several months for complex sites. The water company will not enter into a Section 104 agreement until it is satisfied that the drainage design meets the required standards.
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1. Engage with the water company at pre-planning stage
Contact the local water and sewerage company before or during your planning application. Request a pre-development enquiry to establish sewer connection points, capacity in the existing network, and whether any infrastructure upgrades are needed. This enquiry will also confirm whether the company is willing to adopt surface water sewers and sustainable drainage features on your site.
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2. Design your drainage to Design and Construction Guidance (DCG) standards
All sewers intended for adoption must be designed in accordance with the Design and Construction Guidance (DCG), which superseded the former Sewers for Adoption (8th Edition) in 2020. The DCG sets out pipe materials, diameters, gradients, access point spacing, manholes, pumping stations, and construction methods that the water company will accept. Appoint a drainage engineer experienced in DCG standards.
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3. Submit your drainage design for approval
Submit the detailed drainage layout, hydraulic calculations, longitudinal sections, and construction details to the water company for technical approval. The company assesses the design against DCG requirements and may request amendments. Do not begin drainage construction until design approval is confirmed in writing.
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4. Provide a bond or cash deposit
Before the water company will sign the Section 104 agreement, you must provide a financial security, typically a surety bond from an insurance company or a cash deposit. The bond amount is usually calculated as a percentage of the estimated construction cost and guarantees that the sewers will be completed to adoptable standard even if you are unable to finish the work.
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5. Sign the Section 104 agreement
Once design approval is granted and the bond is in place, sign the Section 104 agreement with the water company. This is a formal legal document. Take legal advice before signing. The agreement will set out the inspection stages, maintenance period, and conditions for vesting.
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6. Construct the drainage to the approved design
Build the sewers, lateral drains, and associated infrastructure in strict accordance with the approved design and DCG standards. Any deviation from the approved design must be agreed with the water company in advance. Unapproved changes may result in the company refusing to adopt the sewers.
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7. Request inspections at key construction stages
The water company will inspect the drainage at specified stages during construction to verify compliance with the approved design and DCG standards. Typical inspection points include trench preparation, pipe laying before backfilling, manhole construction, and testing. Give the water company adequate notice before each stage. Covering work before inspection may require you to expose it again at your cost.
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8. Complete the maintenance period
After the water company confirms practical completion of the drainage works, a maintenance period begins. During this period, you remain responsible for maintaining the sewers, rectifying any defects, and bearing all costs. The water company may carry out further inspections and CCTV surveys during this period.
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9. Apply for vesting
At the end of the maintenance period, apply to the water company for vesting. The company will carry out a final inspection, typically including a CCTV survey. If the sewers meet the required standard, ownership transfers (vests) to the water company. Your bond is released after vesting is confirmed.
Building Regulations drainage requirements
In addition to the Section 104 adoption process, all drainage work on your development must comply with the Building Regulations 2010, specifically Approved Document H. This covers foul water drainage design, pipe sizing and gradients, access points, rainwater drainage, building over sewers, and the requirement for separate foul and surface water systems.
Building control approval is separate from the water company's Section 104 process. You need both. Building control will inspect drainage at key stages, and drains must pass pressure testing before being covered.
Your right to connect under Section 106
Section 104 deals with the adoption of new sewers on your development. Section 106 of the same Act provides a separate statutory right for individual premises to connect to the public sewer.
Where your development has a Section 104 agreement, individual properties will connect to the new sewer network that the water company is adopting. The Section 106 right to connect becomes relevant where properties need to connect directly to an existing public sewer rather than through a new adoptable sewer.
Understanding the distinction between Section 104 (adoption of new sewers) and Section 106 (right to connect to existing public sewers) is important for planning your drainage strategy. The water company can refuse a connection if the drain or sewer is in poor condition or would be prejudicial to the sewerage system, so ensure connections are designed and constructed properly.
Common problems and how to avoid them
Late application
Applying for a Section 104 agreement after drainage construction has started is the most common mistake. The water company may refuse to adopt sewers it has not inspected during construction. In the worst case, you may need to excavate and relay drainage to demonstrate compliance.
Design changes without approval
Changing the drainage layout during construction without the water company's written consent can void the adoption agreement. Always seek approval for variations before carrying out the work.
Surface water drainage disputes
Water companies have historically been reluctant to adopt certain sustainable drainage features such as swales and retention ponds under Section 104. Confirm at pre-application stage which surface water drainage elements the company is willing to adopt. Consider whether alternative adoption routes (highway authority or management company) are needed for specific features.
SuDS requirements
In Wales, sustainable drainage systems (SuDS) require separate mandatory approval from the SuDS Approving Body (SAB). In England, SuDS provision is typically secured through planning conditions. Either way, your surface water drainage strategy must be coordinated with the Section 104 adoption process.
Disputes with the water company
If the water company unreasonably refuses to enter into a Section 104 agreement, you may refer the matter to Ofwat for determination. Before escalating, ensure you have fully complied with DCG standards and addressed all technical objections raised by the company.
What to do next
Once vesting has occurred:
- Confirm vesting in writing - Obtain written confirmation from the water company. Keep this permanently.
- Inform purchasers - Provide evidence of adoption to purchasers' solicitors during conveyancing.
- Check Building Regulations sign-off - Ensure building control has issued completion certificates for drainage work.
- Review surface water arrangements - Confirm any SuDS features not adopted by the water company have long-term maintenance arrangements.
For related guidance, see:
- Flood risk assessment and SuDS compliance - FRA requirements and SuDS obligations
- Construction drainage design and compliance - Approved Document H in detail