Bristol Water has teamed up with pioneering UK-based environmental technology company, Rookwood Operations, to successfully complete a trial to remove harmful phosphorous pollutants from its Chew Valley Reservoir.
While phosphorous is a finite natural resource which is critical for growing food, it can become a pollutant in large quantities in bodies of water like at Chew Valley Lake, driving the growth of harmful algae, degrading biodiversity, and making it harder to treat drinking water.
Having started discussions in late 2023, Rookwood and Bristol Water started the trial of Rookwood’s natural and environmentally friendly Phosphate Recovery Material (PRM) in August 2025 to see if it could safely remove phosphate from Herriotts Mill Pool, which is connected to Chew Valley.
The material is loaded into and deployed in permeable cartridges, filtering water as it flows through the system. As the water passes through the cartridges, the material binds with dissolved phosphate, capturing it before it can enter the wider reservoir.
The process is entirely passive, requires no power, and works with the existing flow of the pool.
Because the installation operates continuously, it removes even very low concentrations of phosphorus, helping to stabilise nutrient levels throughout changing seasons.
Once saturated, the cartridge is replaced, and the phosphate-laden material is removed and repurposed as a slow-release fertiliser - creating a circular, environmentally friendly solution that cleans the water while returning valuable nutrients to land.
The installation successfully demonstrated the material’s efficient ability to absorb and lock away trace amounts of phosphorous in real world conditions, reducing the need for extensive water treatment by removing it from water flowing into Chew Valley Lake.
The system was designed to fit into the existing water structure and to allow the material to interact naturally with the water flowing from between Herriotts Mill Pool and the main section of Chew Valley Lake.
Although simple in appearance, the installation was carefully planned to meet environmental protections and respect the sensitivity of the SSSI-designated area and avoid affecting public use of the site, ensuring the trial was both effective and environmentally unobtrusive.
Liam Pearce, Rookwood Operations’ Chief Commercial Officer, said: “Herriotts Mill Pool has proven that PRM delivers real, measurable improvements in water quality. It consistently removes phosphate, even in low-nutrient periods, and it captures other nutrients too.
This supports healthier ecosystems and helps safeguard the quality of inflows into Chew Valley Lake. Bristol Water’s involvement made it possible, and shows how targeted, nature-friendly interventions can make a real difference.”
Helen Gavin, Environmental Lead at South West Water, said: “Managing the raw water quality of our reservoirs is very important for both treatment and ecological reasons. Overall, the results provide evidence that the material is a practical and sustainable solution that can support Bristol Water’s wider goals for improved water quality and resilience."
Following the success of the trial, Bristol Water and Rookwood are now exploring opportunities for wider deployment across the area.
