Leithen Water (Scottish Gaelic: Leitheann / Abhainn Leitheinn) is a tributary of the River Tweed in Scotland.

It rises in the Moorfoot Hills and joins the Tweed near the town of Innerleithen,[1]: 20  whose name comes from the Scottish Gaelic inbhir, meaning a confluence, and anglicised as "inner" or "inver".

In the summer months, local children build small dams to deepen it, especially at the Cauld (a fish ladder near Innerleithen Golf Course) and at Leithen Bridge.

The latter is an old stone bridge, erected in 1799 using funds from a stipend, to enable easy access for townsfolk to attend church on the west side of the Leithen Water.

The river lends its name to the character Sir Edward Leithen in a number of novels by John Buchan.