Section 106 Drain Adoption Agreements for London Developers

Section 104 Agreements and Sewer Adoption

When a London developer builds a new residential estate or a mixed-use development with multiple properties, the drainage infrastructure serving those properties will eventually need to be either adopted by Thames Water as a public sewer or maintained as a private shared system by the occupiers. Adoption by Thames Water is strongly preferable from the perspective of the future homeowners or occupiers, as it removes the ongoing burden of maintenance and repair from private ownership. The mechanism for achieving this adoption is a Section 104 agreement under the Water Industry Act 1991, named after the section of the Act that gives Thames Water the power to adopt new sewers by agreement with developers.

A Section 104 agreement sets out the technical standards to which the drainage infrastructure must be built, the inspection and testing regime that Thames Water will apply during and after construction, the financial security that the developer must provide to cover the cost of completing the drainage works if the developer defaults, and the process by which Thames Water will inspect, approve, and ultimately adopt the drainage after practical completion. The agreement is negotiated and signed before construction begins, and the drainage must be built strictly in accordance with the agreed drawings and specifications to qualify for adoption.

Section 106 Planning Conditions and Drainage

Section 106 of the Town and Country Planning Act 1990 allows planning authorities to attach legally binding obligations to planning consents, and these obligations are commonly used to require developers to achieve specific drainage outcomes as a condition of developing a site. In London, Section 106 planning obligations may require a developer to contribute financially to Thames Water sewer capacity upgrades, to achieve a specified greenfield runoff rate from the site using sustainable drainage systems, to maintain on-site SuDS features in perpetuity through a management company or residents association, or to dedicate drainage infrastructure for adoption by Thames Water before occupation of the development.

Failure to comply with Section 106 drainage obligations can prevent the granting of a certificate of lawful development, prevent the discharge of pre-occupation planning conditions, or expose the developer to enforcement action by the planning authority. London developers should review their Section 106 agreement carefully at the design stage to identify drainage obligations that will affect the drainage design, the construction programme, and the post-occupation management arrangements for the site.

Practical Steps for London Developers

London developers should engage a drainage engineer at the earliest stage of the design process to assess the drainage adoption strategy for the site. The engineer will advise on whether a Section 104 agreement is required, what technical standards the drainage must meet for adoption, what SuDS measures are required to meet the surface water runoff targets in the Section 106 agreement or planning conditions, and what ongoing maintenance obligations will attach to any drainage infrastructure that is not adopted by Thames Water.

Thames Water has a pre-application service that allows developers to discuss adoption feasibility before submitting a formal Section 104 application, and this service should be used on any scheme where the drainage configuration is complex or where the capacity of the existing sewer network is uncertain. Prestige Engineers can act as drainage consultant on London development projects, preparing Section 104 applications, designing SuDS schemes, and carrying out the CCTV surveys and pressure tests required by Thames Water during the adoption process.