Blackadder Water is a river in Berwickshire in the Scottish Borders area of Scotland, forming part of the River Tweed system. It reached 2.84m at Mouthbridge, which was its highest level ever recorded on Tuesday 22 October 2002 at 2:45pm.

Berwickshire or the County of Berwick is a historic county, registration county and lieutenancy area in south-eastern Scotland, on the English border. The county takes its name from Berwick-upon-Tweed, its original county town, which was part of Scotland at the time of the county's formation in the twelfth century, but became part of England in 1482 after several centuries of swapping back and forth between the two kingdoms. After the loss of Berwick, Duns and Greenlaw both served as county town at different periods.