Whiteadder Water is a river in East Lothian and Berwickshire, Scotland. It also flows for a very short distance through Northumberland before joining the River Tweed. In common with the headwaters of the Biel Water it rises on the low hillside of Clints Dod in the Lammermuir Hills, just ESE of Whitecastle Hillfort and 3 km (1.9 mi) south-east of the village of Garvald.

The River Tweed, or Tweed Water, Scots: Watter o Tweid, Welsh: Tuedd), is a river 97 miles (156 km) long that flows east across the Border region in Scotland and northern England. Tweed cloth derives its name from its association with the River Tweed. The Tweed is one of the great salmon rivers of Britain and the only river in England where an Environment Agency rod licence is not required for angling. The river generates a large income for the local borders region, attracting anglers from all around the world.