Combined sewer overflows


A Water Quality campaign

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Combined sewer overflows


There are approximately 31,000 Combined Sewer Overflows (CSOs) around the UK. Their sole purpose is to discharge untreated human sewage and waste-water when the sewerage system is overloaded. CSOs act as emergency discharge valves in our sewerage system, discharging untreated sewage and wastewater when the system comes close to bursting, supposedly during periods of intense rainfall. Without CSOs, sewage could start backing up in our houses and gardens, so they are a vital part of our sewerage infrastructure. However, SAS is increasingly concerned that they are being used to regularly dispose of untreated sewage, even during times of low rainfall or none at all.

During the 2015 bathing season our Safer Seas Service reported on 926 sewer overflow events across the English beaches in the service. Only 11% of these discharges could have been monitored by the Environment Agency, leaving 821 discharges to impact the environment unchecked.

Surfers Against Sewage sits on a European Commission expert panel reviewing the bathing water directive, Defra’s Cleaner Seas Forum and various regional Bathing Water Liaison Groups.

You can help us lobby the Secretary of State for the Environment calling for more action on the pollution impacting our beaches. We are calling for more urgent action to address on-going sewage pollution at our beaches including:

  • A review of how the UK implements the Bathing Water Directive, ensuring bathing water quality is tested at the appropriate time and in the appropriate place, thus protecting the bathers, surfers and water users most at risk.
  • Increasing water company obligations to introduce more effective and faster investment to remove current sewer overflow assets with priority awarded to sensitive areas such as bathing waters, recreational watersports zones and Sites of Special Surfing Interest.
  • Mandatory year-round sewer overflow warnings introduced for all affected UK beaches regularly used by the public to protect public heath where the current water quality-testing regime fails to.
  • A strict, legally binding limit of 3 sewer overflow discharges per season, per sewer overflow asset. Discharges should only be acceptable in extreme weather events.
  • A ban on water companies installing all new sewer overflow assets directly impacting areas of the coastline important for public recreation or other environmentally sensitive areas.

CSOs are usually hidden out of sight so make sure you check your beach’s bathing water profiles to locate the nearest CSO, and the parts of the beach and bathing water that will be affected when it is discharging. You can find the bathing water profiles on your beaches profile page on the Sewage Alert Service map. Be aware that after periods of rain, CSOs are likely to discharge untreated human sewage and waste-water. And remember, CSOs discharge more frequently outside the bathing season.

Get involved

How can you help with this campaign…

  • Receive free real-time sewage pollution alerts from SAS! Download our Sewage Alerts Service app on iPhone or Android or sign up for our free text alerts service... Learn more…
  • It's important that you report these pollution incidents. If you see signs of a sewage spill call the Environment Agency (EA) pollution hotline on 0800 80 70 60 and the SAS pollution hotline on 01872 555 950. Learn more…
  • Lobby the Secretary of State for the Environment to call for more action to prevent sewage discharges via combined sewer overflows. Learn more…

Campaign timeline

Key campaign dates


Launch of pioneering Sewage Alert Service App

The SAS Sewage Alert Service is now available as an app to download for free on your iPhone or Android smartphone!


Sewage Alert Service

The dramatic expansion of SAS’s pioneering Sewage Alert Service, a real-time SMS service protecting surfers and water users from sewage spills, covering almost 200 surf spots and bathing waters nationwide.