The Ale Water is a tributary of the River Teviot, rising in Selkirkshire and running for most of its course through Roxburghshire, and forming part of the border between them. It is a tributary of the River Teviot.
The river rises at Coutlair Knowe (1,371 feet) in Selkirkshire and flows down from the forest eastwards soon to mark the boundary with Roxburghshire for some distance, before re-entering Selkirkshire. Soon it enters Alemoor Loch, which was a natural lake but which has been expanded by damming the river here to create a reservoir.
Below the dam, the Ale Water meanders amongst the tumble of hills hereabouts and below Wester Rig it takes another turn at marking the county boundary for a mile or so before decisively entering Roxburghshire.
The river's name was originally "Alne".