Horcajo de Santiago Wastewater Treatment Plant, Castilla-La Mancha, Spain

The Horcajo de Santiago wastewater treatment plant is located in the town of Horcajo de Santiago, within the autonomous community of Castilla-La Mancha, Spain. The facility serves a population of approximately 4,500 people, placing it in the small agglomeration category under Spanish and EU regulations. Under the EU Urban Waste Water Treatment Directive (91/271/EEC), plants serving agglomerations of this size are generally required to provide secondary treatment. The plant operates within Spain's national regulatory framework, which transposes the directive and sets standards for effluent quality. The plant discharges treated water into the local watershed, which ultimately drains into the Tagus River basin. The Tagus River flows westward through Spain and Portugal before reaching the Atlantic Ocean near Lisbon. The receiving water bodies support diverse aquatic life and are important for regional water resources.

The plant's treated effluent enters the local drainage network, which feeds into the Tagus River basin. The Tagus is the longest river in the Iberian Peninsula, flowing through central Spain and Portugal to the Atlantic Ocean. The river supports a variety of fish species and provides water for agriculture and urban use downstream. The watershed is ecologically sensitive, particularly in its middle and lower reaches where water quality is critical for biodiversity and human use.