The Primary Filter House, Kempton Park

The Primary Filter House, Kempton Park

This primary filter house was built between 1927 and 1929 by Henry Stilgoe, Chief Engineer for the Metropolitan Water Board. It is constructed of reinforced concrete with a concrete roof and metal windows.

The building has a distinctive plan comprising a central wash water tower flanked by two wings, each containing twelve sand filter tanks. These sit on a raised terrace on either side of a single-storey spinal range that houses outlet weirs and outlet channels. Below ground is a basement engine house and services.

The exterior is symmetrical in composition. The central tower rises through three stages and is slightly battered. It is flanked by single-storey six-bay ranges which sit raised above partly concealed tanks and basements. Central steps lead between a pair of rectangular battered pavilions featuring channelled rustication in roughcast concrete, with three vertical recessed panels above. These pavilions are set forward from higher outer bastions of the filter house terrace. The entrance consists of a pair of part-glazed panelled timber doors within a timber frame, set in a flat, low-relief concrete architrave with a panel above inscribed with "Metropolitan Water Board". Crittal windows flank the entrance and appear in the upper stages, recessed within three vertical channels. The uppermost stage is set back with a recessed parapet, formerly housing the wash water tank.

The north and south elevations repeat this theme with pairs of triple vertical channels housing recessed Crittal windows. The west elevation mirrors the east. Battered pavilions at the inner and outer angles of the filter house terrace form quadrants, each with six external tanks. The six-bay single-storey spinal range emphasizes its outer and inner bays as tower forms, with tripartite windows in plain openings on three elevations. Many of the original Crittal windows have been replaced with timber casements or fixed lights. The bays between follow a broader rhythm of alternating roughcast panels and tripartite windows, again with former Crittal windows largely replaced.

Internally, a central splayed staircase with piers and retaining walls of reconstituted stone features incised fielded panels on the outer faces, with buff reconstituted stone skirtings and copings. The concrete framework of the tower retains the concave seating for former compressed air cylinders. The middle stage contains a well-lit gallery with two arcades of concrete piers supporting the former wash water tanks at the upper stage, positioned behind the parapet. The longitudinal ranges are supported on a pair of cranked arcades with slender concrete shafts, flanking a filtered water outlet channel within a parapet wall. Similar outlet weirs serve each bay. The parapet walls, dados and skirtings are lined in green glazed tiles. Longitudinal inspection galleries run along each flank.

Preliminary filtration had been used from the early twentieth century, with rapid filters first introduced by the Metropolitan Water Board in 1926 at Walton. The filters at Kempton Park were constructed after a Triple Expansion Engine house increased the volume of water arriving at the site, performing preliminary filtration before water passed to the slow sand filter beds. The filter tanks were washed out using compressed air blown through them, pressurized by the head of wash water in the central tower. Kempton Park was the first installation to employ the patented compressed air cleaning method, which necessitated the expressive central tower. As part of a nationally important water-processing complex, this is an exceptionally monumental public utilities building of the 1920s with a strong architectural presence.