Sewage discharges

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.

How many sewage discharges occur?

In 2024 there were around 450,000 recorded sewage discharges from storm overflows in England, lasting around 3.6 million hours.

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, and by the end of 2023 all storm overflows had monitors fitted.

Source: Environment Agency, Event Duration Monitoring – Storm Overflows – Annual Return (long-term trends dataset)

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.

Source: Environment Agency,  Event Duration Monitoring – Storm Overflows – Annual Returns

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.

This data is also presented on the Commons Library interactive sewage discharges dashboard. This allows users to select data by constituencies, catchment areas, or water companies, and to look at details of discharges for individual storm overflows.

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 2035 and eliminate these by 2050. Achieving these targets relies on investment by water companies, as reducing discharges requires infrastructure improvements.

Further measures to monitor storm overflows, as well as to increase penalties for pollution incidents, were introduced by the Labour Government in the Water (Special Measures) Act 2025. In March 2025, the Environment Agency published new guidance on its storm overflow assessment framework, which sets out the technical details for water companies to investigate and improve individual storm overflows.

In addition to this, the government has appointed Sir Jon Cunliffe, former governor of the Bank of England, to chair an Independent Commission on the water sector regulatory system. The results of this commission are expected to inform further policy and legislation.  

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.