How do you solve a problem like CSOs?

23 April 2021


Combined Sewer Overflows (CSOs) are a thorn in many a side. This antiquated system, which falls under the responsibility of the water industry and is regulated by the Environment Agency, was designed to prevent homes and businesses from flooding during extreme weather. It acts as a pressure release valve, allowing excess water into rivers and the sea to prevent sewers overflowing. But what can be done when one person’s protection is another’s pollution? Anglian Water’s Head of Environmental Quality, Dr Lucinda Gilfoyle, explains…

“The reason CSOs were originally built was to protect homes and businesses from flooding. Under extreme weather conditions they prevent sewers from becoming overloaded, acting as the pressure release that allows floodwater to escape into a river or the sea, and not back up into the toilets and shower trays of ground floor bathrooms. Because of the job they do, and despite calling them ‘sewer overflows’, most of the water they release is rainwater, not raw sewage.


“CSOs were created at a time when society understood a lot less about the environment than it does today. Many CSOs are decades old. Today, as an industry, we know they are not a suitable solution to deal with the issue of overloading of a sewer network. At Anglian Water, we’ve been working through them for years, and fixing them where they cause problems. This isn’t new and it isn’t something that is driven by the recent media or political coverage. It’s because we don’t think they are fit for purpose and we want any issues with them resolved. We must do this in a prioritised way however, as the engineering solutions are not straightforward and the cost to customers is significant. So, we address those posing an environmental risk first and are working through the rest.


“But although they have been in place for many years, the spotlight is increasingly falling on them, and the perception of the damage they do.


“Each of our CSOs has been assessed for the environmental risk potential, as defined by the Environment Agency, and they have each been permitted to act as a ‘storm overflow’. But despite being consented by our regulator, it is understandable that no one finds it acceptable that even extremely diluted sewage reaches our rivers. As an industry we must do (and are doing) more to address the problem.


“Nobody is trying to hide behind ‘regulatory permits’, though. To do so might, at best, come across as a benign neglect for the environment. At worst, it might look like water companies simply not caring. The truth is quite the opposite - at Anglian Water, we care very deeply. So much so that in 2019 we became the first utility company to have consideration of wider social and environmental impact written into our Articles of Association - the legal documents that underpin the foundation of our business. We are bound to consider the impacts of what we do on the environment and the communities we serve. These aren’t just words – it's an obligation we’ve placed on ourselves.


“However, fixing CSOs is not the silver bullet for improving all river water quality. In truth, storm overflows account for just 4% of all the reasons for rivers and waterways not achieving the best water quality. As is clear from Environment Agency river quality data, there are many contributing factors outside of water company control that cumulatively have a more significant impact on the health of our waterways. This is a problem that reaches much further than the water industry alone and so much more needs to be done if we are to achieve our aspirations on the quality of UK waterbodies. A focus on CSOs alone isn’t enough.


“We are going to do our bit. So, how do we plan to solve a problem like CSOs – and why can’t we just simply rip them all out?


“The cost of replacing assets like CSOs with new systems and flood mitigation (as properties still have to be protected from flooding) would run into many billions. Customer bills would rise dramatically, not to mention the disruption caused by completely replumbing the major cities in our region. We have a responsibility to strike a balance between making the vital investments needed in sustainable services and resilience for the future while keeping bills affordable for all.  The process of removing CSOs cannot be achieved overnight. And when you throw in other challenges like climate change and investing to negate future water deficit, too – what you end up with is a real conundrum.


“So what are we doing? We’ve installed Event Duration Monitors (EDMs) on more than 700 of our CSOs, and plan to have them in place across all CSOs by the end of 2023. The EDM initiative is aimed at improving the visibility of what CSOs are doing, to identify which ones are spilling too frequently and making all this information public. Clear data on when and for how long these assets spill will enable us to target investment to the assets that most need attention. This approach has worked well for our coastal CSOs, to protect bathing water quality in our region for over eight years now.


“Our EDM programme is many, many times larger in scale and ambition than our coastal programme, and with any new technology comes the challenge of ensuring it’s set up to be as accurate as possible. Because this monitoring system is so new (and because we’re asking it to work in quite a hostile environment), we’ve seen quite a lot of erroneous data – some of which has been reported in the press.  In some cases, the technology has triggered hundreds of hours of ‘spill data’ that simply hasn’t happened. And this can be verified by our technicians, who visit any unusual alerts at our sites to check if the equipment is operating correctly. We are rectifying this,  and should see a marked improvement in future data sets. We see the system as a really positive move as this data will allow us to target future investment in CSOs accurately.


“Unflushables are another significant cause of harmful environmental impacts and are often a reason for overflows operating. Simply put, sewer blockages caused by wet wipes, sanitary items, fats and grease are one of the main causes of sewer flooding in homes and the environment.  This is one of the reasons that we have led the promotion of the ‘fine to flush’ branding for moist tissue products that don’t contain plastic and can be safety flushed away.


“We all want accurate information and targeted investment where it will have the most impact. And most importantly, we all want healthy rivers. We’re committed to tackling CSOs. But it will take a joined-up approach from others too – landowners, highways teams, housing developers and customers – to help stop run off from roads and fields, to divert rainwater away from sewers, and to stop putting unflushable items down the drain, ultimately preventing blockages, to make a real difference to our waterways. The issue of CSOs is important, but it must not become the sole narrative when it comes to safeguarding UK rivers. There is a real risk that if all investment is targeted here we will never realise the improvements we all want, and our rivers have waited so long to see."