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Search any UK location to check nearby Combined Sewer Overflow (CSO) locations before you buy, plan or develop near a watercourse.
Updated: periodically as source data is republished · Last checked by Maplify: July 2026
This layer maps Combined Sewer Overflow (CSO) locations across England, sourced from Environment Agency and water company published datasets. Each overflow is shown as a point marking where untreated sewage mixed with rainwater can discharge into a watercourse during heavy rain, to prevent sewer flooding.
Storm overflow activity has become a high-profile environmental issue, with frequency and location of discharges increasingly scrutinised by regulators, campaigners and local communities. Proximity to a frequently discharging CSO can be a material consideration for riverside or coastal sites, and connecting new development to the sewer network can itself affect overflow frequency.
Storm overflow marker
Combined Sewer Overflow (CSO) location, often shown with associated monitoring data.
Sites near frequently discharging storm overflows may attract closer scrutiny under water quality and environmental protection policy, particularly for schemes affecting drainage or requiring new outfalls. Confirming formal capacity and drainage strategy requirements with the relevant water company is standard due diligence for development near a watercourse.
Check for nearby storm overflows and available discharge frequency data.
Review a site-specific drainage strategy where the proposal is near a watercourse or existing sewer network.
Check the Flood Risk and Rivers, Lakes & Water layers for the same site for the fuller picture.
This is general guidance, not professional or legal advice — confirm specifics with the relevant authority or a qualified professional.
Environmental Consultants
Scope drainage and water quality assessments near watercourses.
Property Developers
Screen riverside and coastal sites for storm overflow proximity.
Planning Consultants
Advise on likely conditions relating to drainage and environmental protection.
Storm overflow checks are commonly run alongside these related layers.
What is a storm overflow (CSO)?
A Combined Sewer Overflow releases untreated sewage mixed with rainwater into a watercourse during heavy rain to prevent sewer flooding — their frequency and location are increasingly scrutinised for environmental and amenity reasons.
Why do developers check nearby storm overflows?
Frequent discharge activity near a site can be a material consideration for riverside or coastal development, and connecting new development to the sewer network can affect overflow frequency.
Does this layer show discharge frequency?
Where available, storm overflow data can include monitoring information — check the Environment Agency's published event duration monitoring data for the most current discharge statistics.
How often is storm overflow data updated?
Data is sourced from Environment Agency and water company published datasets and is checked periodically as new extracts are published.
Open the map, generate a site report or save your search to come back to it later.
| Provider | Environment Agency / Water Companies |
| Geometry type | Point |
| Coverage | England |
| Update schedule | Periodic check against published extracts |
| Reference date | July 2026 |
| Licence | Open Government Licence v3.0 |
