Thames Water has appointed Costain to design, build and upgrade two treatment assets in Sandhurst, Berkshire and Selborne, Hampshire.

The award, valued at more than £5 million for the two sites, will see Costain support Thames Water's upgrading of wastewater treatment assets as part of its Wastewater Asset Assurance Programme (WAAP). The schemes are the first that have been awarded to Costain as part of a wider investment programme for sewage treatment sites (STWs). This could see up to 25 similar projects allocated to Costain to create cost-efficient infrastructure solutions for Thames Water.

The planned construction will involve implementing flow monitoring technology to validate flow-to-full treatment for wastewater before it is discharged, upgrading the existing screening operations at the inlet station, improving storage tank capacity and revising the storm return pumping systems. The work will improve the ability of both sewage treatment works to treat the increasing volumes of incoming sewage, reducing the need for untreated discharges in wet weather. The schemes are due to complete in 2025.


Thames Water is currently undertaking its largest ever upgrade of sewers and STWs, with plans to improve more than 250 sites in the coming years as part of a £1.12bn investment in its wastewater sites.

Gerard Shore, Water Director at Costain, commented: "Thames Water is investing in river health and has a clear plan to upgrade hundreds of treatment plants across the region. This will have a transformative impact on the lives of residents and local communities. We know we can add considerable value by identifying further opportunities at the outline design stage to maximise efficiencies for the upgraded treatment infrastructure. This will help ensure that these assets are fit for purpose for the long term."