Soane sent to Wimpole's clerk of works, Henry Provis, working drawings fot the water house on 26 July 1793, probably drawing 15 (Journal N^o 2).

The water reservoir has a hexagonal external plan surrounding a circular chamber that measures 20 feet in diameter at ground level. A domed roof rests on a stepped drum over the inward-leaning walls. The exterior has pedimented projecting bays alternating with inward-tilted panels. The water house was made of renderd brick and plaster; on drawing 15, a signed agreement between Soane and John Bayley confirms the design to be executed. Thomas Poynder was the bricklayer (D. Stroud, p.760).

The building is shown in a topographical perspective, plan and section published in Soane's Sketches in Architecture, 1793 (plates 41 and 42) and referred to as a 'Castello d'aqua'. It was built to replace an earlier conduit head standing just north-east of the house, at the southern end of Lancelot 'Capability' Brown's eastern ride (D. Stroud, p. 760). Water would be directed to the house from here via various pipes. The building is modelled on a Roman type placed at the edges of the city where Roman aqueducts would have terminated, distributing water pipes into town. Soane's design draws it influences from Roman mausoleum architecture. It is a simplified version of a design Soane worked on in 1779 for the annual competition, the 'Concorso', at the Academy in Parma in Italy.

The water house was demolished in the 19th century, although its foundations were excavated in 2002 (D. Adshead, 2003, p. 15).