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What are sewage discharges?

Sewage discharges are the release of raw, untreated sewage into watercourses, such as rivers. These discharges often take place through storm overflow valves, designed to release water from the sewer network when the volume of water is too great for it.

Some use of storm overflows is permitted, to avoid the sewer network becoming overwhelmed and risking sewage backing up into homes and businesses. However, it has been alleged that many water companies are using storm overflows far more regularly than they ought to.

In 2023 there were 464,056 recorded sewage discharges from storm overflows in England. Together they lasted 3.6 million hours. All overflows had monitors fitted by the end of 2023.

The overflow monitoring system started in 2016 when there were fewer than 1,000 monitors reporting data. Since then, the number of functioning monitors has increased to more than 14,000.

Table showing trends for England in the number of sewage storm overflows monitored, total spills, their duation and the average number/duration of spills per overflow from 2016 to 2023

The increased number of monitors means that changes in the total number of spills over time will be dominated by the increased coverage of recorded data, obscuring any underlying changes in discharges.

Adjusting discharge data for the number of monitored overflows gives a better indication of trends, but it is still a limited measure and patterns are closely linked to changes in rainfall.

Charts showing the average number and duration of sewage spills per overflow in England, 2016-2023. Trends have been variable with peaks in 2019 and 2023.

While the latest EDM data gives a much more complete picture of the number and duration of discharges from storm overflows, it still has limitations. These include the lack of reliable information on trends, no information on the volume of sewage discharged and that it only includes sewage discharged from permitted overflows, not any leaks from the rest of the system.

What are the plans to address sewage discharges?

Sewage discharges have negative environmental and health impacts, such as altering river chemistry, making wildlife ill, and resulting in illness for people who use polluted waters recreationally, such as wild swimmers.

The government has set targets for itself, water companies, and regulators in its Storm Overflows Discharge Reduction Plan, which aims to reduce sewage discharges. This calls for increased monitoring of storm overflows, and sets targets to reduce the use of storm overflows by 2025 and eliminate these by 2050. Achieving these targetst relies on investment by water companies, as reducing discharges requires infrastructure improvements.

All UK political parties have expressed a desire to decrease the volume of sewage entering the UK’s watercourses, but several factors (including the design of the sewage network, the regulatory process, and the enforcement capacity of environmental regulators) make this difficult to achieve.

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