Guidance: Storm overflow assessment framework 2025
Summary
The Environment Agency has published a 2025 update to its storm overflow assessment framework for water companies in England. The guidance replaces the 2018 version and clarifies how spill data, valid year averages, water quality impact assessments and cost-benefit considerations should be applied under the Urban Waste Water Treatment Regulations.
Why it matters
Storm overflow performance and related wastewater infrastructure can affect development viability, environmental risk assessments and due diligence on residential sites. Surveyors may need to be aware of the updated framework when considering drainage, flood risk and local infrastructure constraints.
Key points
- 2025 framework replaces the 2018 storm overflow assessment guidance
- Applies to water companies in England under Urban Waste Water Treatment Regulations requirements
- Clarifies use of spill data, including incomplete EDM data and VYA resets
- Updates stage 2 water quality impact assessment and flowchart
- Adds appendix on Population Equivalent and further BTKNEEC cost-benefit guidance
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