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CSO Combined Sewer Overflow


Water Utility Sewerage Networks

In 1989, at the time of UK water industry privatization, over 23,000 combined sewer overflows (CSOs) had been identified. CSOs owned and operated by UK water companies are regulated by the Environment Agency (EA) in England and Wales, the Scottish Environment Protection Agency (SEPA) and the Northern Ireland Environment Agency (NIEA). For the foreseeable future it will be unrealistic to totally eliminate discharges from CSOs, in terms of cost, logistics and disruption. Since 1990 over 6000 of the CSOs with the highest pollution risk have been either improved or replaced, while around 4000 sites have been identified as posing little risk. This still leaves a significant number which require effective monitoring.