Sewage spill data for 2024: what’s in our Hertfordshire waterways?

Across Hertfordshire, untreated sewage was discharged for 19,234 hours in 2024. This was 11,406 hours more than in 2023 – a huge rise of 146%. This is completely unacceptable and we continue to call on water companies, Councils and the Government to do more to stop this pollution of our waterways.

Sewage continues to overflow into our waterways, and despite pronouncements by regulators, Government and water companies, the situation is getting worse not better.

How do sewage spills come about?

Sewage spills into our waterways when the storm overflows in our sewerage network are automatically activated by heavy rainfall or flooding. These storm overflows are a safety valve designed to prevent sewage from backing up into properties or onto streets, and they have been part of the sewerage network since it was first built. But with some sewage treatment works at or near their full capacity, the storm overflows are activating more frequently.

Overall 2024 data for England

Nationally, untreated sewage was discharged for a record total of 3,614,427 hours through storm overflows, 8,558 hours more than in 2023.

The Rivers Trust, in their State of our Rivers 2024 report found that rivers across England are in a desperate state of affairs. No single stretch of river in England is in good overall health. Just 15% of English river stretches reach good ecological health. And toxic chemicals that remain in ecosystems for decades pollute every stretch of English rivers. (A river stretch is a short length of a river where measurement takes place.)

The 2024 data for Hertfordshire

CPRE Hertfordshire has analysed the Government’s sewage spill (‘event duration monitoring’) data for 2024. This is available from the Environment Agency and is also mapped by The Rivers Trust and Top of the Poops.

There was significantly more sewage spilled into our waterways in 2024 than in 2023, which in turn experienced more sewage spills than in 2022. The trend is going in completely the wrong direction.

Across all of Hertfordshire last year, there were over 1,500 spills resulting in the release of raw sewage into our waterways, for a total duration of over 19,000 hours, or the equivalent of 800 days’ continuous flow.

This affected all of our Hertfordshire chalk streams and rivers, many of their tributaries, and our three canals: the Grand Union, the Lee Navigation and the Stort Navigation.

The places with the greatest number of hours of sewage spills are shown here, in descending order by number of hours. (Source: Environment Agency)

Cottered tops the league table once again, as it did in both 2023 and 2022. With 3,648 hours of sewage spilling into Cottered Brook, that is over 40% of the time all year.

Markyate, Maple Lodge and Berkhamsted sewage treatment works are also high in the hall of shame, causing huge amounts of pollution in the River Ver, the River Colne and the Grand Union Canal respectively.

Is the data reliable?

There are caveats with this data. Not all of the event duration monitoring sensors are completely accurate all of the time. And the data only reflects storm overflows. A year ago the BBC conducted an investigation into England’s water companies discharging sewage when the weather is dry. The investigation suggests 6,000 possibly illegal spills occurred during 2022.

You can also see what’s happening currently at your local sewage treatment works, on the Sewage Map UK.

Sewerage infrastructure is a crucial planning issue

We believe the damage being done to our rivers and their habitats has reached crisis point. The 2024 data show that existing sewerage infrastructure is wholly inadequate to cope with current, let alone future population.

This is currently being tested at the High Court, with a case at Maids Moreton in neighbouring Buckinghamshire. The BBC reports that the Council has granted permission to add 153 new homes to the existing community of 350 houses. But the local sewage works has been over capacity for years, causing sewage overflow spills into the nearby River Great Ouse. Wildfish, an environmental charity that campaigns against river pollution, is pursuing a judicial review at the High Court, challenging the Council’s decision to grant planning permission. Wildfish says the case goes to the heart of the gap between plans for new housing and the capacity of the existing sewage infrastructure.

And we agree. With huge housing growth proposed across Hertfordshire, the sewerage infrastructure is now a crucial planning issue right here.

For example, the Maple Lodge sewage treatment works near Rickmansworth handles the sewage from Hemel Hempstead. The government data shows 1,916 hours of sewage spills in 2024, which is about 20% of the time all year. Yet Dacorum Borough Council and St Albans District Council are proposing 11,000 new dwellings at ‘Hemel Garden Communities’ in spite of the evidence suggesting that the sewerage capacity just isn’t available.

Another example is the Rye Meads sewage treatment works, which handles much of the sewage from eastern Hertfordshire. But it is located immediately adjacent to the Lee Valley RAMSAR wetland site, which is a designated protected wildlife site of international importance. East Hertfordshire District Council has allocated sites for 10,000 new dwellings nearby around Gilston, and we question whether this is consistent with the legal imperative to protect the RAMSAR site.

What are we doing about this?

We continue to call on Local Planning Authorities (Councils) –

• To use ‘pre-commencement’ planning conditions to prevent development from taking place until sufficient sewerage provision has been made for that specific development. This could include reinforcing the sewerage network, extending treatment capacity at a sewage works, improving surface water drainage, and reducing storm sewage overflows into the environment.
• To require developers to demonstrate that adequate sewerage infrastructure is in place before the first dwellings are occupied.

We also call on Government –

• To give the Environment Agency the power to veto planning applications for which adequate sewerage infrastructure cannot be provided by the completion date of the first dwellings. This includes sewerage infrastructure provided by the developer and that provided by the sewerage company.
• To hold the Environment Agency to account for missed response time targets for investigating sewage spills.
• To put tighter restrictions on water companies to prevent sewage spills including holding these companies to account for managing storm overflows in line with legal and regulatory requirements.
• To require water companies to be transparent about their current sewerage operations and future programmes for sewerage provision including information on planned projects.

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CPRE Hertfordshire, the countryside charity, campaigns for the local countryside for everyone to value and enjoy. We are a small charity and depend entirely on memberships and fundraising to support our work. Membership is open to all, and it’s quick and easy to join online. Please join us today.