Biggar Water is a river in Lanarkshire and Peeblesshire, in the Southern Uplands of Scotland.
It forms part of the River Tweed system. It rises, as Biggar Burn, in the north-east of the parish of Biggar, South Lanarkshire and flows about generally south-westerly toward the town of Biggar, where it becomes Biggar Water. It then flows about eastwards before its confluence with the Tweed mile north-east of Drumelzier in Peeblesshire.