The course of the Douglas Water is entirely within the South Lanarkshire council area.
The river rises in the hills which separate Lanarkshire from Ayrshire, to the south west of Muirkirk. The source is close to that of the River Ayr, which flows west to the sea, but the Douglas Water runs north-east then east, past Glespin and into Douglasdale. Here the river flows through the village of Douglas, and past the scant remains of Douglas Castle. The castle was a stronghold of the House of Douglas, a powerful medieval family who took their surname from the river. The A70 road follows the river through Douglasdale, and on to the Clyde.
East of Douglas, the river passes under the M74 motorway, just south of the Happendon services, and turns toward the north-east again. Below the village of Rigside, the smaller Poniel Burn flows into the Douglas Water. Beyond this confluence is the small village of Douglas Water. A dismantled railway line runs between the river and the A70 for the remaining 2 miles (3 kilometres) of its course. The Douglas Water flows into the Clyde around 3 mi (5 km) south of Lanark.
- Ordnance Survey: Landranger map sheet 71 Lanark & Upper Nithsdale (Map). Ordnance Survey. 2014. ISBN 9780319229712.
- "Ordnance Survey: 1:50,000 Scale Gazetteer" (csv (download)). www.ordnancesurvey.co.uk. Ordnance Survey. 1 January 2016. Retrieved 18 February 2016.
- James, Alan. "A Guide to the Place-Name Evidence" (PDF). SPNS - The Brittonic Language in the Old North. Archived from the original (PDF) on 13 August 2017. Retrieved 25 November 2018.
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