Thames Water has announced that Cirencester Sewage Treatment Works (STW) is currently undergoing a £21 million upgrade to improve the quality of effluent released at the works and increase the site’s capacity to help manage the challenges of climate change and prepare for population growth.

The STW, which can currently treat up to 269 litres of wastewater per second, will almost double its capacity to 484 litres per second. This includes a new 9000 square metre HIRB, a natural filtration system that provides a final treatment of water prior to it being returned to the environment.


The HIRB will treat an extra 114 litres of waste per second, as part of the treatment process. Increasing this capacity will greatly reduce the risk of storm overflows during periods of heavy rainfall and return a better quality of effluent to the river.

Having started the upgrade in Summer 2023, work is currently ongoing and is expected to be completed in Spring 2025. This comes as part of Thames Water’s commitment to updating infrastructure and playing its part to contribute to improving the health of rivers and waterways.

Paul Parfrey, Project Manager at Thames Water said: "We are pleased to be working towards improving our Cirencester Sewage Treatment Works for residents and businesses in the area. Our new 9000 square metre HIRB will treat an extra 114 litres of waste per second, to help increase capacity of the site.

"As custodians of this important infrastructure we need to ensure our sites are resilient to the pressures of climate change and population growth so we can continue to provide reliable services to our customers. This upgrade to our network will help protect customers and the health of the rivers and waterways."