The Belfast Water Commissioners was a public body in Ireland and later Northern Ireland, established by the Belfast Water Act 1840, to improve the supply of water to the expanding city of Belfast. By 1852, the city was suffering a shortfall in supply of almost one million gallons per day. In 1889 the body's name was changed to Belfast City and District Water Commissioners in recognition of the expanding boundaries of Belfast and resulting increased demand for water.

The Mourne Conduit was a water main which ran 42 kilometres (26 mi) from the Silent Valley Reservoir to Carryduff, near Belfast and was built between 1893 and 1901 for the Belfast City and District Water Commissioners. This was supplemented by additional pipelines twice in the 20th Century. This system supplied water to Greater Belfast and North Down for more than 100 years. It is labelled as the Mourne Aqueduct in Ordnance Survey maps from the early 20th century.