Immortalised by Robert Burns as ‘Sweet Afton’, the Afton Water flows gently down the picturesque Glen Afton and on through the centre of the village of New Cumnock before joining with the River Nith. The name afton simply means ‘water-course, river’ and derives from one of the common Celtic forms as summarised by W.F.H Nicolaisen .
afon (Welsh, Cumbric)
abann (Old Irish);
auon (Cornish, Breton)
The name Afton appears to be of Welsh, Cumbric origin as opposed to Gaelic that tends to yield the harder sounding ‘v’ containing names such as Avon in Avondale, now Strathaven (i.e. an equivalent of Glen Afton) .
The element water when applied to a water-course, as in Afton Water, is in Scotland indicative of a water-course that is smaller than a river but grander than a burn or ‘pol-‘. However, the element is little used locally and the river is simply known as ‘the Afton’ and Glen Afton is simply ‘up Afton’.
The Rev. James Johnston  suggests Afton Water, New Cumnock is probably Gaelic abh don ‘brown stream‘, far removed from Burns ‘crystal stream’.