 Since 1973 Plymouth has been supplied water by South West Water . Prior to the 1973 take over it was supplied by Plymouth County Borough Corporation . Before the 19th century two leats were built in order to provide drinking water for the town . They carried water from Dartmoor to Plymouth . A watercourse , known as Plymouth or Drake 's Leat , was opened on 24 April 1591 to tap the River <unk> . The Devonport Leat was constructed to carry fresh drinking water to the expanding town of Devonport and its ever growing dockyard . It was fed by three Dartmoor rivers : The West Dart , <unk> and <unk> . It seems to have been carrying water since 1797 , but it was officially completed in 1801 . It was originally designed to carry water to Devonport town , but has since been shortened and now carries water to <unk> Reservoir , which feeds most of the water supply of Plymouth . <unk> Reservoir is located about 5 miles ( 8 km ) north of the city and was constructed in 1898 and expanded in 1928 . 
