To ask His Majesty's Government whether water companies are required to have full and complete maps of their sewage network infrastructure, and if so how this is enforced.

Having a full and detailed map of sewerage assets is a vital part of understanding the network and identifying areas for improvements. Water companies are already required to map their assets under Section 199 of the Water Industry Act 1991. The section, and the requirement to map assets, is enforceable under powers laid out in Section 18 of the Act. Sewerage undertakers are not required to keep records of assets that were laid before 1 September 1989, but only if either:

1) the undertaker does not know of, or have reasonable grounds for suspecting, the existence of the drain, sewer or disposal main;

2) it is not reasonably practicable for the undertaker to discover the course of the drain, sewer or disposal main and it has not done so.

As part of the Environment Act 2021, a new duty has been created for sewerage undertakers in England to produce Drainage and Wastewater Management Plans (DWMPs). DWMPs set out how a sewerage undertaker intends to manage and improve their drainage and wastewater systems over the next 25 years. DWMPs will complement existing requirements to map the sewerage network, to facilitate a detailed understanding of the network and help ensure that drainage and wastewater services are better managed and properly supported, as well as delivering greater efficiencies for customers and supporting investment in nature-based solutions.

In addition, the Storm Overflows Discharge Reduction Plan sets out that the Government expects that water companies have maps of their sewer networks, to understand where properties with separate rainwater pipes are connected to their combined sewer network.