The Silent Valley Reservoir is a reservoir located in the Mourne Mountains near Kilkeel, County Down in Northern Ireland. It supplies most of the water for County Down, surrounding counties and most of Belfast. It is owned and maintained by Northern Ireland Water Limited (formerly DRD Water Service). The reservoir was built between 1923 and 1933 by a workforce of over 1,000 men, nine of whom died during construction. History In 1891, the Belfast Water Commissioners (BWC and later the Belfast City and District Water Commissioners or BC&DWC) hired Luke Livingston Macassey to investigate options for a source of an additional water supply for the expanding city of Belfast. Macassey selected the Mourne Mountains for the reasons summarised in a 1935 report:The portion of the Mourne Mountains acquired by the Commissioners totals approximately 9,000 acres. It is all mountainland [sic], uninhabited, and a large part of it is rocky and precipitous. It extends from about 330 feet above sea-level to a maximum of 2,796 feet above sea-level, Slieve Donard being the highest mountain within the area. It is practically devoid of trees, being covered with heather, gorse, and bracken where not granite rock and boulders. The average rainfall on the area is 57.6 inches per annum. It is drained by two streams : on the west, the Kilkeel river flowing due south, and the Annalong river, lying parallel to and to the east of the Kilkeel river, draining the Annalong Valley. The catchment of the Kilkeel river is 5,500 acres in extent, that of the Annalong river being 3,500 acres. The water of both these rivers is similar and of excellent quality, having 2 degrees of hardness. Private Acts of Parliament (in 1893, 1897 and 1899) allowed the BC&DWC to secure the catchment area with associated access and water rights. At the time the catchment was capable of providing some of water per day, however as this much was not required immediately, a three phase approach was followed: The first stage was to divert water from the Kilkeel and Annalong rivers through the newly constructed Mourne Conduit to a reservoir at Carryduff. These water pipes were capable of supplying of water per day. Work was completed in 1901. The second stage was to build a storage reservoir, the Silent Valley Reservoir, across the Kilkeel River. Design work on this phase began in 1910, but procurement of the work was delayed