A S104 (Section 104 of the Water Industry Act (1991)) agreement is a legal agreement between a developer and a water company, where the developer agrees to build sewers to an agreed standard, which the water company will then adopt. The agreement is usually signed at the early stages of the development and lasts for several years, until the water company is satisfied the network has been completed to their satisfaction.
Section 102 of the Water Industry Act (1991) allows a developer or an individual to submit an application to a water company asking them to adopt a private operational sewer which is already installed. On a new development, the S102 process is usually followed if the new sewers are installed and become operational before the S104 agreement is signed and the S104 process is no longer applicable.