We get faultless service on the river (5)
I believe the answer is:
weser
'the river' is the definition.
(German river)
'we get faultless service' is the wordplay.
'get' is a charade indicator (letters next to each other).
'faultless service' becomes 'ser' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'we'+'ser'='WESER'
'on' acts as a link.
Can you help me to learn more?
(Other definitions for weser that I've seen before include "Er, sew up the German river" , "German runner" .)