CSOs: protecting homes, businesses and wider environment

Storm water drain

The environment is, quite rightly, at the top of our customers’ agenda – and it’s at the top of ours, too.

Something that’s been in the news a lot recently are CSOs – Combined Sewer Overflows – and the impact they may be having on water quality and the environment in and around our rivers and seas.

In the UK, years of local development of the surrounding environment, rapid growth in population, and the impact of climate change have added significant pressure to the network.

We take the issue of releases from CSOs very seriously, particularly because we know our customers are use the waters in and around the south coast more frequently for leisure activities.

However, it’s important to understand not just why CSOs exist, but what we’re planning to do about reducing the need for them and the actions we’ve already taken.

Why CSOs exist

The combined sewer system and the attached overflows have played an essential role since the turn of the 20th century in preventing contamination of drinking water and the protection of homes, public buildings such as hospitals and schools, and wastewater treatment works from flooding.

During or after a period of wet weather, combined sewers can become overwhelmed by rainwater (surface water) entering our network from road and roof run off (in some case >95% of the water entering the system).

In order to protect public health, people’s homes and public property (like schools and hospitals), flooding of the environment and to protect the operation of the wastewater treatment works, this excess water has to be released to watercourses.

What is released is not accurately described as "raw sewage" but wastewater, which includes water from washing machines, showers, dishwashers, etc, heavily diluted by surface water which is rain and run-off from roads and land.

The released water is also likely to have passed through a screen at the treatment works to remove large solids and is also likely to have passed through a storm tank in which solids settle to the floor of the tank.

These controlled releases are permitted by the Environment Agency, and part of the design of the sewers inherited by water companies from local authorities in the 1970s. But the use of CSOs is now far more complex than first intended.

Tackling the need for CSOs

It’s important to know that CSOs in the UK are not just a water industry problem.

While we know water companies have a vital role to play, it will require multisector collaboration and investment to reduce or stop the use of CSOs.

We’re fully supportive of the Government’s cross-body Storm Overflows Taskforce, which is looking at this issue right now. The scale of the challenge means it would take up to 25 years and around £100bn of investment to phase out use entirely.

Clearly, the issue won’t be solved overnight and will need to be tackled in a comprehensive and integrated way, with authorities and key organisations – not just the water industry – working together.

We believe preventing surface water from entering sewers is the most economical way to safeguard capacity in the network, reduce the amount of storm overflow releases, delay the need for new investment and reduce the need for carbon intensive treatment of clean surface water.

A joint effort

So we’re working closely with the farming community on projects such as sustainable drainage systems and nature-based solutions, as agriculture is the largest source (40%) of pollution in rivers. We’re also working with other contributors like industry, transport networks, and local authorities to better manage surface water.

That’s why we recently hosted a summit for leaders of 16 national and local organisations with an interest in improving the water quality and natural habitats of Chichester and Langstone Harbours.

Chaired by Professor Sir Dieter Helm, former independent chair of the natural Capital Committee, it was agreed that a co-ordinated and integrated programme of action underpinned by collaboration and partnership, is critical to faster and more effective progress to tackle the urgent threat to the natural capital of the harbours, and the increasing pressure of climate change and population growth.

We’re also making a number of improvements ourselves. In the short term, we’re investing £1.7bn over 2020-25 to improve capacity and capability of our wastewater network. Work to improve storm overflow management includes: Event Duration Monitoring (EDM) already installed at 98% of sites with further improvements being delivered to close the coverage gap before 2023; improved flow management at wastewater treatment works where we’ve invested £13m between 2015 and 2020 to address risk to storm overflow at 29 sites and we are investing a further £13m between 2020 and 2025 at a further 36 sites to improve either instrumentation or data capture or both.

Like other water companies we have also increased transparency by publishing a wide range of environmental performance data. Our online storm release notification system, Beachbuoy, helps our customers and partners by providing near real time information about CSO activity at designated bathing waters and recreational watercourses. Beachbuoy currently covers all 83 designated bathing waters in our region and 2 recreational harbours and includes granular data on releases from individual CSOs.

The use of CSOs is a huge, complex, expensive, but important issue. Most of our employees live on the south coast and also enjoy the fun and relaxation our coastline, rivers and wildlife offer. They’re the teams that are working on this, and we’re committed to improving our environmental performance. Tackling the use of CSOs is a big part of that. And we’re ready for the challenge.