The number of discharges from combined sewer overflows (CSOs) in 2021 highlight the scale the of the challenge the water sector faces to meet targets set by Defra this week to cut spills by 80% by 2050.
Data from event duration monitors (EDMs) supplied by water companies and published by the Environment Agency showed 372,533 from 14,470 combined sewer overflows last year.
The average number of spills from each CSO was down from 33 in 2020 to 29 last year.
On average, 89% of CSOs have an EDM attached and since the passing of the Environment Act all CSOs must be monitored by the end of 2023.
United Utilities had the highest number of recorded spills last year at 540,753 from its 2,192 CSOs, while Welsh Water reported the fewest at 3,567 from its 124 CSOs.
To date 86% of CSOs have returned data from EDMs, which is around 12,400 monitors. This marks a rise from 8,276 in 2019.
“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,” said James Bevan chief executive of the Environment Agency.
“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,” Bevan added.
Increasing transparency by monitoring the number and duration of spills from overflows is an essential step towards reducing harm from them. Regulators and government have said they will hold water companies to account on their work to significantly reduce the reliance on CSOs.
This week the government proposed eliminating the impacts from 75% of overflows at the most environmentally sensitive locations and 70% fewer discharges into bathing waters by 2035. By 2040 Defra wants to see 40% of all emissions reduced and 80% (approximately 320,000) eliminated by 2050.
Under the Environment Act companies will be required to provide near real-time information on storm overflows based on data from EDMs to monitor water quality, especially close to wastewater treatment works.
Combined sewers were standard until the 1960s when surface water from rain and highways was separated from wastewater systems. However, the legacy of these combined systems means hundreds of thousands of kilometres of sewer networks that can be overwhelmed by surface water at times of heavy rain. CSOs are used to discharge from the networks to prevent flooding in homes but contribute to the poor health of rivers in England and Wales.
Separating the systems has been estimated to cost between £350 billion and £600 billion and cause widespread major disruption to access pipework under towns and cities.