Combined Sewer Overflows and the Race to Meet Environmental Standards
Combined Sewer Overflows (CSOs) have long been a challenge for water utility companies, and with the ongoing WINEP obligations across the industry, the pressure to minimise the damage of storm overflows is greater than ever. Utilities are increasingly held accountable for environmental damage, facing regulatory scrutiny, public outrage, the constant threat of fines for non-compliance and even imprisonment.
While the industry looks for solutions to manage overflows, the need for pace in implementing the solutions is clear.
In this blog, we explore the state of water companies navigating the challenges, using innovative technology to streamline workflows and drive long-term improvements in storm overflow management.
Storm Overflows: The state of today
What are storm overflows and why are they used?
Storm overflows, also known as Combined Sewer Overflows (CSOs), are systems designed to release excess wastewater and stormwater from combined sewer systems directly into nearby water bodies, such as rivers, lakes, or the sea. These systems are typically used during periods of heavy rainfall or storm events when the volume of water exceeds the capacity of the sewage treatment plants or the sewer system itself.
What is the issue with storm overflows?
“At present, there is public concern that storm overflows are operating when there has not been significant rainfall. The current levels of harm caused by storm overflow discharges into rivers and seas cannot continue, and the wastewater companies must tackle this.” — Ofwat
The issue with storm overflows is that they are discharging untreated wastewater into rivers and seas, sometimes even without significant rainfall, raising public concern. While intended to prevent urban flooding during heavy rainfall, this practice contaminates water bodies, harms ecosystems, and poses risks to public health.
With climate change increasing the frequency of storms and flooding (Met Office), the reliance on storm overflows has grown. However, this has drawn criticism as water companies face pressure to adopt more sustainable solutions to reduce environmental damage and meet stricter regulatory standards, especially with AMP8 approaching.
State of the industry today
Key messages of the Water company performance report 2022-23
- Water companies need to accelerate actions to reduce pollution incidents to meet the 30% reduction that they committed to over the 2020-25 period
- While many water companies have made progress in reducing leakage, more improvement will be needed if the sector is to meet the 16% reduction that it committed to in the 2020-25 period.
- Water companies have overspent their total water and wastewater allowances. However, many companies have not spent their enhancement allowances.
- Customer satisfaction continues to fall. Improving this should be a key priority for all companies.
Industry accountability and the pressure to innovate
As regulatory bodies like Ofwat place increasing pressure on water utilities to reduce sewage spills, the need for faster, more efficient options selection becomes paramount. Industry rankings and accountability metrics are now closely tied to how effectively water companies manage storm overflows and CSOs.
Despite these challenges, CSO incidents continue to occur at a high rate, making it clear that the current approach is no longer enough. Water companies are embracing technology to optimise storm overflow management and improve their accountability standings to meet the growing pressures.
3 solutions to storm overflows:
- Sustainable Urban Drainage Systems: Sustainable Urban Drainage Systems (SuDS) help manage excess stormwater by using natural processes, like permeable surfaces and green spaces, to absorb and slow water flow. These systems reduce the pressure on sewers, minimising the need for storm overflows and enhancing local flood resilience.
- Water Treatment Plant Upgrades: Upgrading water treatment plants increase their capacity to handle larger volumes of stormwater and sewage. Advanced technologies, such as enhanced filtration and treatment processes, improve the system’s ability to treat wastewater efficiently, reducing the frequency and impact of storm overflows. However these can take years to go through planning and build. Subsequently temporary systems need to be used as a placeholder until such upgrades can be put in place.
- Temporary Solutions: Temporary solutions, such as storage tanks and mobile treatment units, can be deployed to store or treat excess wastewater during storm events. These provide a stopgap measure, allowing systems to handle surges without discharging untreated sewage, while long-term infrastructure upgrades are implemented.
Case Study: Accelerating Workflows for CSO Site Assessments
A real-world example of how Sensat is transforming CSO leakage mitigation can be seen in a recent project with a UK water utility company. By utilising Sensat’s platform, the company leveraged digital workflows to create new modern standards of inspecting 96 potential CSO sites in just one day. This task would traditionally have taken weeks, if not months, using traditional methods of site inspections and surveys.
This updated workflow leverages a visual environment to consolidate all key data, enabling faster and more accurate inspection of potential sites. It is estimated to have saved the water company hundreds of thousands of pounds over a three-month period.
Learn about Severn Trent’s Visionary Partnership with Sensat
Looking ahead: the future of storm overflow management
To achieve long-term sustainability and compliance, companies must embrace technology that enhances their ability to manage CSOs efficiently and effectively. Platforms like Sensat are leading the charge in this space, providing the tools necessary for water utilities to make data-driven decisions, reduce costs, and meet regulatory expectations.
With AMP8 approaching the water industry know that they not only need to put in temporary stopgaps, but also prioritise innovation.