Thames Water has announced the completion of a £17.4 million upgrade at Buntingford STW. Having started work in 2022, the water company completed the upgraded in November 2024 which has expanded its flow capacity by 20%.
This upgrade will greatly reduce the risk of storm overflows during spells of heavy rainfall and longer periods of groundwater retention, which can cause the sewer systems to be overwhelmed.
As part of the upgrade, the site has also implemented a phosphorus reduction scheme, which will improve the quality of effluent released into the river following treatment.

Rob Hales, Senior Project Manager at Thames Water said:
“As custodians of 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. Our upgrades at Buntingford sewage treatment works, come as part of our commitment to help protect customers and the health of the rivers and waterways.
“We believe all discharges are unacceptable and we are committed to seeing healthy and thriving waterways, however we can’t do it alone. While we play an important role in this, we aren’t the sole custodians of river health. We need everyone working together to help our waterways thrive.”
The upgrade of Buntingford STW is part of Thames Water’s plans to improve 250 of its wastewater sites to help manage the effects of population growth and climate change. These include nearby sites at Bishop Stortford, Little Hallingbury and Harpenden. You can see a list of upgrades here.