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 adwaters 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.The stream wends its way south east for approximately where it joins with the Faseny Water to form the Whiteadder Reservoir created in 1968, which supplies most of the towns of East Lothian (including Cockenzie power station) and Berwickshire, with water.From there, crossing into Berwickshire it runs alongside the B6355 road to Ellemford where it joins the Dye Water and further on at Abbey St. Bathans, the Monynut Water.By this point having become a much larger body of flow, the Whiteadder meanders across Eastern parts of the Merse passing the communities of Preston, Chirnside, Allanton. Here at Allanton the Whiteadder joins with its antonymic counterpart the Blackadder Water. The river proceeds by Foulden, Edrington, and Paxton, it crosses into England, before joining the River Tweed, just north of East Ord, a suburb of Berwick-upon-Tweed.