The Environment Agency has published updated guidance for water companies on preparing their Drainage and Sewerage Management Plans (DWMPs).

Preparation, publication and maintainance of a Drainage and Sewerage Management Plan is now a statutory requirement for the water companies. The Environment Act in 2021 gave DWMPs a new legal status, which means they will have a greater role in directing future investment

The first cycle of DWMPs were published in 2023 and completed against separate guidance. The latest documents provide updated guidance for developing DWMPs based on lessons learned from the first cycle of plan development, and to provide up-to-date guidance now that DWMPs have become statutory.

The aim of the guidance – which is not exhaustive - is to assist the water companies in developing plans that comply with relevant statutory obligations and with government policy relating to DWMPs.

Key areas covered in the guidance include:

• Legal requirements
• Available capacity
• Current and future demand
• Current and future resilience
• Measures to take or continue
• Using nature-based solutions
• Relevant environmental risks and how to mitigate
• Alignment with flood risk management planning

Requirements the water companies must address in setting out what their DWMPs include:

• the capacity of the drainage and sewerage system including wastewater treatment works and sewer capacity
• the ability of their network to carry surface water and flood waters during high rainfall and other extreme weather
• an assessment of the current and future demands on the drainage and sewerage system
• the resilience of the drainage and sewerage system
• the measures the company intends to take or continue for the purpose of meeting the statutory obligations
• the likely sequence and timing for implementing those measures
• relevant environmental risks and how those risks are to be mitigated
• the impact of climate change on the performance of assets and, consequently, the capacity of the system

Guidance has particular focus on asset health

The guidance has a particular focus on asset health, stating that the companies should consider the role of the full extent of their assets, including wastewater treatment works, and consider the risks to the service they are required to deliver, including lack of capacity, asset or system failure, defined as “poor asset health’. Asset health is defined as the capability of drainage and sewerage assets to meet service requirements whilst maintaining their physical condition, in consideration of both current and future operational and environmental factors.

Other issues the guidance says the water companies should consider include:

• the operation, maintenance and enhancement of systems and assets to meet current and future challenges
• how they have proactively engaged with the local authority when considering solutions to improve asset performance, including options for partnership working.

The guidance also says they should how they have proactively engaged with the local authority when considering solutions to improve asset performance, including options for partnership working. In addition, they should recognise that current poor asset health and poor operational performance can reduce the design capacity of the drainage and sewerage system.

Current and future demand and resilience

When assessing the current and future demands on their drainage and sewerage systems, they should consider the condition of assets and their ability to cope with:

• both existing demand and the projected future demand based on population growth calculations
• known planned development in their area such as new towns or major urban development
• the effect of climate change and other risk factors such as extreme weather

Referring to the Cabinet Office (2011) “4 R’s” for resilience -Resistance, Reliability, Redundancy, Response and recovery, the guidance states:

“Your DWMP must address the current and future resilience of your drainage and sewerage system. To do this, you should understand your assets and plan and act appropriately to deliver short and longer-term resilience.

“Maintaining and improving resilience will require you to identify and manage a complex range of risks to make sure your assets operate effectively to meet current and future service needs. This includes the successful management of assets, which are often intergenerational in life, and operational systems on a day-to-day basis while also ensuring mitigations are in place to manage the impact of low probability, high impact events.

“These core company activities are vital to the effective operation of a wastewater system but may not be obvious or visible to customers or wider stakeholders….

“You should consider resilience of your assets and systems to external stresses, including all sources of flooding and coastal erosion, climate extremes, power outages and other utility failures, for example mobile communication outages.”

While the guidance says the focus of DWMPs should be on assets owned by the water companies, it points out the plans should also consider the communities and landscapes in which they are situated and the impact of other drainage systems and pathways on the performance of systems (and vice versa) to ensure the companies understand and effectively manage the risks ‘to’ and ‘from’ your their systems.

“Understanding these interactions will need collaboration with other Risk Management Authorities and alignment of the development of your DWMP with their drainage management and flood risk management strategies.

“Such partnerships present enhanced opportunities to manage the targeting and removal of surface water from the combined adopted sewerage network in a more sustainable manner, as well as providing opportunities to co-create interventions with other RMAs to deliver wider community benefits.”

The Water (Special Measures) Act which came into effect in February 2025 also introduced an additional requirement for DWMPs which will require the water companies to address the use that will be made of nature-based solutions, technologies and facilities within their drainage and sewerage system. The Government intends to commence the requirement later this year which will apply in respect of the new round of DWMPs.

The guidance also states:

“In England, the most recent version of the Storm Overflows Discharge Reduction Plan (SODRP) is a key driver for investment in drainage and wastewater systems and your DWMP should reflect the targets and outcomes of this plan.”

Click here to access the guidance online