Horley STW Wastewater Treatment Plant, Reigate and Banstead, Surrey

Horley STW is a wastewater treatment plant located in Horley, within the Reigate and Banstead district of Surrey, England. The facility serves a population of around 35,600, making it a medium-sized agglomeration under UK and EU classifications. The plant is situated near the town of Horley, close to the border with West Sussex. As a UK wastewater treatment plant, Horley STW operates under the Water Industry Act 1991 and is regulated by the Environment Agency. For agglomerations of this size, secondary treatment is typically required, and in sensitive areas, tertiary treatment may be mandated. The treated effluent from Horley STW is discharged into local watercourses that eventually drain into the River Mole, a tributary of the River Thames. The Thames flows through London and into the North Sea. The plant plays a key role in protecting the water quality of the River Mole and downstream ecosystems, including the Thames estuary, which supports diverse aquatic life and is an important ecological corridor.

Horley STW discharges into the River Mole, which flows northward to join the River Thames near Hampton Court. The Thames then meanders through London before emptying into the North Sea via the Thames Estuary. The River Mole is a chalk stream that supports diverse aquatic life, including brown trout and various invertebrates. The plant's operations help maintain water quality in this sensitive river system, which is part of the Thames Basin and subject to conservation efforts for its ecological value.