Environment Agency publishes Event Duration Monitoring data for 2021

Almost nine in ten storm overflows now have monitoring devices providing vital information about their use to hold water companies to account and drive environmental protections, data published today (31 March) shows.

The data is published on the same day that the government has launched new targets to deliver the largest programme to tackle storm sewage discharges in history, with a consultation now live.

Under the proposals put forward in the consultation:

  • By 2035, the environmental impacts of 3,000 storm overflows (75%) affecting our most important protected sites will have been eliminated;
  • By 2035, there will be 70% fewer discharges into bathing waters;
  • By 2040, approximately 160,000 discharges, on average, will have been eliminated (40% of the total); and by 2050, approximately 320,000 discharges, on average, will have been eliminated (80% of the total);
  • Water companies will be encouraged to accelerate these timelines wherever possible while preventing unnecessary costs for consumers.

Some 12,400 monitors (86%) have returned data for the 2021 Event Duration Monitoring release published by the Environment Agency. This is up from 8,276 in 2019 and follows Environment Agency action to ensure water companies install monitors on the vast majority of storm overflows by the end of 2020.

All storm overflows will have monitors by the end of 2023, supporting the Environment Agency and Ofwat in holding water companies to account.

The 2021 data also shows:

  • The average number of spills per storm overflow was 29 times in 2021, compared to 33 times in 2020;
  • 5% of storm overflows recorded spills of 100 times or more in 2021; and
  • 13% of storm overflows did not spill in 2021.

The EA has also driven significant improvements to expand the level of detail provided in this year’s publication to make it more consistent and accessible. The data now includes grid references for each overflow and enables water companies to explain the primary reason for frequent spills and what they plan to do to resolve these.

Environment Agency Chief Executive Sir James Bevan said:

“Water companies have rightly been under increasing pressure from the Environment Agency, campaigners and the public for allowing far too many sewage spills into rivers, and we are holding the industry to account on a scale never done before. Sewage pollution can be devastating to human health, local biodiversity and our environment.

Requiring water companies to provide this data is critical in ensuring everyone can see what is going on. I am pleased that we are on course to have all overflows monitored by next year, but the present situation is simply not good enough. Water companies need to act now to reduce their overflows to the minimum possible.”

Storm overflows are designed to release excess storm water from the sewerage system into rivers or the sea during prolonged, heavy rainfall, to ensure they are not overwhelmed. Water companies should only do this under strictly permitted conditions.

The latest data shows that water companies have been discharging sewage into waterways far too often, and that there is no room for complacency. Increasing transparency around the use of storm overflows is fundamental to efforts across government and by regulators to understand and improve water quality, and crucially to hold water companies to account.

EDM data has informed the EA’s major criminal investigation into potential widespread non-compliance of water and sewerage companies at wastewater treatment works.

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.

Water companies are also under a duty to secure a progressive reduction in the adverse impact of sewage discharges. These legally binding obligations will help reduce pollution in rivers, protecting wildlife and public health.

Event Duration Monitoring dataset can be read here.



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