Thames Water's £21m Cirencester Upgrade: Doubling Capacity to Protect Local Rivers

Thames Water is making a significant investment of £21 million to upgrade its Cirencester sewage treatment works (STW), a key project that will nearly double the site’s capacity and significantly improve the quality of effluent released into local rivers. This initiative is part of the utility’s broader efforts to modernise infrastructure and address the growing challenges of climate change and population growth.

What’s happening: The Cirencester STW, which currently treats 269 litres of wastewater per second, is being upgraded to handle 484 litres per second. A central feature of this project is the construction of a new 9,000 square metre high infiltration reed bed (HIRB).

This natural filtration system will add the capacity to treat an additional 114 litres per second, providing a final treatment stage before water is returned to the environment.

By increasing capacity, the upgrade is expected to significantly reduce the risk of storm overflows during heavy rainfall, a persistent issue for local waterways like the Churn, Thames, and Coln.

Why it matters: This upgrade is part of Thames Water’s larger plan to enhance 250 wastewater sites across the region, including other locations in the Cotswolds.

By improving the resilience of the Cirencester STW, Thames Water aims to ensure that the site can manage increased demand while also protecting local rivers from pollution.

Local officials, including Gloucestershire County Councillor Lisa Spivey, have praised the project, expressing hope that the new reed bed will reduce the frequency of harmful sewage discharges, which have been a common problem during storm events.

Looking ahead: The Cirencester upgrade is expected to be completed by Spring 2025. In parallel, Thames Water is preparing for a major £240 million upgrade to its Oxford STW, which will address similar issues on a larger scale.

This upcoming project will focus on enhancing treatment processes and expanding capacity to meet stricter environmental standards. Thames Water has already alerted the market to this significant contract opportunity, with a formal notice expected in early October .