Source of Thames produced water for river (5)
I believe the answer is:
tweed
'river' is the definition.
(I've seen this before)
'source of thames produced water' is the wordplay.
'source of' suggests taking the first letters.
'produced water' becomes 'weed' (as in urinated).
The initial letter of 'thames' is 't'.
't'+'weed'='TWEED'
'for' is the link.
(Other definitions for tweed that I've seen before include "Flower on border" , "Fabric; river" , "Flow" , "Twilled cloth" , "Rough material" .)