UK Gov Releases 2022 Event Duration Monitoring Data

The Environment Agency has today (31 March) published Event Duration Monitoring data for 2022. This includes data from all 10 water and sewerage companies (WaSCs) operating in England, with information on the frequency and duration of storm overflow spills.

Event duration monitoring data was returned from 13,323 storm overflows during 2022 - with the duration and frequency of sewage spills now monitored at 91% of storm overflows across the country. This is up from 12,707 in 2021 (equating to 89% coverage).

The government has instructed water companies to install monitors on all storm overflows by the end of this year.

While the data shows a 19% reduction in the number of sewage spills - down from 372,533 in 2021 to 301,091 spills in 2022 - this is largely due to last year's below average rainfall. The data also shows that in 2022:

  • The average number of spills per storm overflow was 23, compared to 29 in 2021;
  • 3% of storm overflows spilled more than 100 times, compared to 5% in 2021; and
  • 18% of storm overflows did not spill at all, compared to 13% in 2021.

Storm overflows are a safety valve designed to release excess storm water from the sewerage system into rivers or the sea during periods of rainfall and/or snowmelt to ensure they are not overwhelmed. Water companies should only do this under strictly permitted conditions. EDM devices provide essential information about storm overflow use, helping to hold water companies to account.

The Environment Agency shares public concerns around storm overflows and is calling for urgent improvements in storm overflow maintenance, management and investment by water companies.

Environment Agency Executive Director John Leyland said:

The decrease in spills in 2022 is largely down to dry weather, not water company action.

We want to see quicker progress from water companies on reducing spills and acting on monitoring data.

We expect them to be fully across the detail of their networks and to maintain and invest in them to the high standard that the public expect and the regulator demands.

Water Minister Rebecca Pow said:

The volume of sewage being discharged into our waters is unacceptable and we are taking action to make sure polluters are held to account.

By bringing in comprehensive monitoring - up from just 7% in 2010 to the most extensive level ever now being at 91% - this government and its regulators have enabled the extent of sewage discharges to be revealed, so that we are better equipped to tackle this challenge.

We have set the strictest targets ever on water companies to reduce sewage discharges, and are requiring them to deliver the largest infrastructure programme in their history - an estimated £56 billion in capital investment over the next 25 years, driving more improvements. This is the game-changing action that will make the difference we need.

The Environment Agency will be carrying out further assessments of the latest data, which will inform the planning of the Water Industry National Environment Programme for the next round of water company environmental improvements in the 2024 price review (2025 to 2030).

The data has also informed the development of the new duties brought in by government under the Environment Act 2021, including a new duty on water companies to publish near real-time information on the operation of storm overflows and to monitor the water quality upstream and downstream of storm overflows and sewage treatment works.

Storm overflows account for 7% of waterbodies failing to reach Good Ecological Status - a significant part of the 36% which fail due to impacts from the wider water industry. Agriculture accounts for 40% of failures, while urban and transport pollution makes up 18%.

The full data releases for 2022 and previous years are available on

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