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 south-east of the village of Garvald.