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Milestone storm overflow data shows there's more to do

Looking ahead to the official release of storm overflow monitoring data Stuart Colville gives the industry perspective on the expected fall in spills.

  • There were fewer overflow spills last year into rivers and seas, and the average spill was shorter
  • The length of overflow spills reduced by a third, while the number of individual overflow spills fell by a fifth
  • £3.1billion of work is happening up and down the country to cut spills

15,000 overflows were built into sewers between the 19th century and the 1960s. Our forebears’ idea was that these would act as ‘relief valves’ during storms, allowing excess rainwater from drains to escape before pipes overloaded and flooded bathrooms. The concept was similar to an overflow in a sink.

This dubious legacy brings with it two problems. First, these older sewer pipes carry not just rainwater but also sewage, creating a dilute but deeply unpleasant mix. Second, the destination for that mix when escaping through an overflow is typically a river (with a smaller proportion going into the sea).

Over the last thirty years, the water industry has improved 7,000 overflows. But much more of its attention has been focussed on cleaning sewage from treatment works - as the biggest cause of harm to fish and other species, that’s where regulators directed most of their targets and so where most money was spent.

Those efforts achieved real and important results for beaches, and steep reductions in the most important river pollutants like ammonia and phosphorus. But they also entirely missed the public’s increasing (and entirely legitimate) clamour for action on spills into rivers. The urgency of that call has increased to the point where it couldn’t be clearer that the country expects more.

In coming days the Environment Agency is expected to publish an important update on the number of storm overflow spills going into our rivers and seas. They have already collected data from monitors, and will release an official verdict before the end of the month, with breakdowns by company.

We have analysed the same records, and calculated that there were fewer overflows last year. The duration of each spill was also shorter.

Specifically, we expect the data to show that, across England in 2022, there was:

  • A 34% reduction in the time overflows spent spilling, compared to the year before.
  • A 19% reduction in the number of times an overflow spilt
  • An average of 22 spills per overflow, down from 29 times per overflow the year before.

Looking at those numbers, it looks like:

  • These reductions are consistent with industry’s work to reduce spills by a quarter over the next couple of years, and steeper targets for future years beyond that
  • About half of all overflows last year operated in line with the Government’s “backstop” target for 2050, with ten spills or fewer over the year.

These reductions are hugely welcome, and particularly important in a year when species were terribly affected by drought. However, 2022 still saw around 1.75million hours of spills (down from about 2.7million the year before), leaving a colossal amount of work still to do if industry is to fully meet the public’s expectations.

These results are an important milestone, but leave a lot more to do. Companies are spending £3.1billion on overflows between 2020 and 2025, and have committed to bring them down by a quarter over that period. That is leading to unprecedented activity right across England, as this map from Government shows:

However, it is also important to note that many regions of England saw below-average rainfall last year. This is likely to have reduced pressure on sewers. While the location, intensity and duration of rain are all important factors in determining spill numbers, and effects will vary by region, the dryness of a year does have a significant influence and last year’s numbers will reflect that.

Taking a step back, industry is clearly at an inflection point on overflows. The issue is receiving levels of investment and energy that totally dwarf the preceding century and a half of efforts. Looking at companies’ emerging plans for future years, it is clear that this is only going to grow further.

There are two priorities for industry now: first, to get on with the actions needed to build progress, delivering targets as quickly as possible; and second, to expand transparency by building on recent announcements by Thames Water and South West Water in other regions.