Water Supply Scheme, one of the most important engineering works and items of public infrastructure in Australia, and still has the longest wall of all the NSW water supply dams. It was designed by the NSW Public Works Department under the direction of one of Australia's leading water supply engineers, E.M. De Burgh. The completion of the Cordeaux Dam was a significant step in the continuing process of providing a reliable water supply for Sydney and surrounding areas as part of the Upper Nepean Scheme. Even by the international standards of the time, Cordeaux was a large dam and was a significant work of engineering in its day. It continues to play an important role as a major source of supply for the Sydney region. Cordeaux Dam is a handsome, well proportioned structure with strong Egyptian style architectural character which complements the monumental nature of the structure and its attractive natural surroundings. Cordeaux Dam includes a range of ancillary structures which form components of the overall site, including residential cottages of various ages for operational staff, one of which appears to date from the construction of the dam. This latter is associated with the Residential Engineer for construction and operation of the dam and is a fine example of a late Federation Bungalow style building. The other residences are representative of their age and type. The public picnic grounds and gardens attached to the Cordeaux Dam contain a cultural landscape resource - including remnants of its interwar period plantings, layout and detailing, and extensive areas of bushland. There is evidence in the landscape design, particularly in the use of palms and tree ferns and battered stonework retaining walls, of an intention to continue the Egyptian Revival references apparent in the design of the main dam structures. Cordeaux Dam was listed on the New South Wales State Heritage Register on 18 November 1999 having satisfied the following criteria. The place is important in demonstrating the course, or pattern, of cultural or natural history in New South Wales. Cordeaux Dam is constructed within the Upper Nepean catchment area which was developed with the completion of the Cataract and Nepean tunnels in 1888, as the fourth source of water supply for Sydney. The potential of the Upper Nepean Catchment Area to supply water was fully developed through the construction of four major dams between 1903 and 1936. Cordeaux Dam is the second of