A Section 104 agreement (s104) is a legal agreement made under Section 104 of the Water Industry Act 1991 between a developer and the local sewerage undertaker (water company). It provides for the construction and subsequent adoption of new foul and surface water sewers, pumping stations, and associated infrastructure serving a development.

Once adopted, the sewerage infrastructure becomes the responsibility of the water company to maintain, repair, and operate in perpetuity. This transfers the long-term maintenance burden from the developer (or a management company) to the statutory undertaker.

The s104 process typically follows these stages:

Pre-planning: Early engagement with the water company to establish connection points, capacity, and design requirements
Detailed design submission: Sewer layout, pipe sizes, gradients, manholes, flow control devices, and attenuation storage designed to Sewers for Adoption standards (now Design and Construction Guidance)
Technical approval: The water company reviews the design for compliance with their requirements
Agreement execution: The legal agreement is signed, typically requiring a bond or cash deposit
Construction: Sewers are built under the supervision of the water company’s inspectors
Maintenance period: Usually 12 months of trouble-free operation before final adoption
Vesting certificate: The sewers are formally vested in the water company

Key design requirements for s104 adoption include:

Minimum pipe diameters (typically 150mm for foul, 225mm for surface water)
Minimum and maximum gradients for self-cleansing velocity
Manhole spacing, construction, and access requirements
SuDS components eligible for adoption (this varies between water companies)

Aegaea coordinates s104 applications as part of our surface water drainage design service, ensuring that drainage infrastructure is designed to be adoptable from the outset.

Section 104 Agreement