Johnston's Creek Sewer Aqueduct is a heritage-listed sewage aqueduct located in Hogan Park, off Taylor Street, Annandale, Inner West Council, Sydney, New South Wales, Australia. It was designed by William Julius Baltzer, an engineer in the NSW Public Works Department, and built by the Department in 1897. The property is owned by Sydney Water. It was added to the New South Wales State Heritage Register on 18 November 1999. History The Johnstons Creek sewage aqueduct was constructed in 1897. The aqueduct was constructed as an extension of the Bondi Ocean Outfall Sewer which was then known as the Northern Main Sewer. This sewer carried sewage from the densely populated inner-western suburbs of Balmain, Annandale and Glebe. The sewer necessitated the crossing of the 'Johnstone's Creek Valley' and 'White's Creek Valley' to deliver the sewage to the ocean outfall junction at the Junction of Parramatta and City Roads. The Northern Main Sewer was one of the Board's early major sewer schemes. The section of Northern Main Sewer, which embraces the aqueducts across Johnstone's and White's Creeks, was constructed under Government Contract No. 77 (basically the area between Catherine Street and Minogue Crescent). The design work for this contract was completed by early 1895, and which proposed the sewer be carried on mass concrete and brick arches and a lattice bridge. This scheme was subsequently abandoned in favour of using a carrier and supporting arches of reinforced concrete construction, the contract for which was let in mid 1896. The engineer credited with the design is W. J. Baltzer, an engineer in the Sewerage Branch of the Department of Public Works. Baltzer, a graduate of a German university, worked for the firm Carter Gummow & Co. which held the patent rights for the Monier system of reinforcing concrete. Carter Gummow & Co. were instrumental in bringing reinforced concrete construction to the fore. The design provided for a sewer carrier internally U shaped in section 3-ft. 6-in (1m.) by 4 ft. 6-in (1.37 m) constructed in reinforced concrete. The sewer carrier is supported by a series of reinforced concrete arches: There are 8 large spans, each of 81-ft 10-in (25 m.) centre to centre with a clear span of 75-ft (23 m.), and a number of smaller subsidiary arches at the eastern edge. The total length is 924-ft. (281.6 m.). Each of the arches is seated on mass concrete piers. It was repaired during