Combined Sewer Overflows – from challenge to opportunity
Combined Sewer Overflows (CSOs) operate as a pressure valve in our sewerage sewer systems designed to protect properties from sewers that when overwhelmed by rainfall can cause sewage to back up into our streets and properties causing flooding. CSOs are used to spill excess sewage into watercourses and the bathing water. The environmental risks as a consequence of CSO spills are likely to grow as a result of urbanisation, climate change and the ageing of our sewerage infrastructure. CSO spills can be associated with poor quality rivers and bathing waters and have recently attracted public and media scrutiny and outrage.
Subsequently the government released a Stormwater Overflow Discharge Reduction Plan in August 2022 and approaches to reduce CSO spills are a key part of the Water Industry National Environment Programme (WINEP) and the first round of the Drainage and Wastewater Management Plans (DWMPs). The management of CSOs are going to be a key feature of the industry’s investment plans for years to come and are likely to be one of the most significant areas of future investment for the water industry. Approaches to managing CSO spills include optimisation of the sewer system, building additional storage, reducing the amount of rainfall entering the drainage system through approaches like retrofitting Sustainable Drainage and sewer separation. Effectively and sustainably tackling CSO spills will require collaboration between water companies, local authorities, highway authorities and those managing urban drainage, surface water infrastructure and our places and spaces.
Learning Outcomes:
Attendees will…
- Gain a shared understanding of the purpose of CSOs both at the treatment works and in the network
- Have a broad understanding of approaches to monitor and regulate CSO spills
- Understand and describe some options for managing CSO spills and the benefits to be achieved
- Appreciate collaborative approaches to planning and delivering solutions to manage CSO spills

This training is now full. Registration is closed.
Should you have any questions or enquiries regarding this training, please email learning@ciwem.org.