Former Filter House, Banagher Glen, Dungiven, Co Londonderry

The building is a former filter house, constructed between 1920 and 1939, and situated in Banagher Glen, Dungiven, County Londonderry. It is an example of a utilitarian structure, notable for its marvellous setting within a densely wooded glen containing streams, waterfalls, and diverse birdlife.

The building is a long, single-storey structure built of insitu concrete. The entrance gable, approximately 10 metres wide, features a central pair of narrow, square-headed doors flanked by piers, with a flat concrete canopy supported on projecting side walls. An entrance platform, originally accessed by steps (now missing), is a thin concrete slab resting on three splayed concrete brackets. The roof has a 25-degree pitch, with moulded projecting false concrete purlins that previously secured the timber bargeboards; most of the deep timber barge is now missing, and a wooden finial sits at the gable apex. The ground slopes steeply across the width of the gable. The concrete walls display formwork joints and have a painted finish. The long wall facing north-east and the Owenreagh River is 12 bays long. This wall has no windows, but includes a high, wide sliding door and three narrow, square-headed door openings, some secured and constructed as gables. Shallow recessed areas are incorporated into the wall. The eaves line of the first two panels is higher than the remainder of the roof. Gutters are missing. The wall is painted and bears a large mural depicting water being gathered in a reservoir, filtered, and ultimately arriving at a large tap; the mural is by Brush Strokes of Garvagh. The roof is covered with corrugated sheet metal, with long lengths of patent glazing at ridge level. The remaining walls are similarly constructed and lack murals.

The filter house is contemporary with the nearby reservoir, dating to 1934. It ceased operation in 1968 when new water treatment works were built on Caugh Hill. Inside, the filter house contained 21 closed cylinders, each 2.7 metres in diameter and filled with filtering sand, along with air compressors, chemical pumps, and Pelton wheels to provide power. The building is situated at the lower end of the steeper section of Banagher Glen, which is now a nature preserve with limited public access. Landscaping, including car parks and picnic areas, has been undertaken around the filter house; the site is generally pleasant but somewhat overgrown. Former settling ponds are located adjacent to and downstream of the building. The structure is of industrial archaeological interest.