Water supply for part of Thurso? (5)
I believe the answer is:
forth
'water' is the definition.
(I've seen this before)
'for part of thurso?' is the wordplay.
'part of' suggests taking the first letters (I've seen 'part' mean this).
'thurso?' becomes 'orth' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The initial letter of 'for' is 'f'.
'f'+'orth'='FORTH'
'supply' acts as a link.
Can you help me to learn more?
(Other definitions for forth that I've seen before include "running into view" , "Scottish river and firth" , "Water" , "Edinburgh's river" , "River and estuary in eastern Scotland" .)