Disconnect midlands from English water supply (6)
I believe the answer is:
severn
'english water supply' is the definition.
The definition suggests a singular noun which matches the answer.
'disconnect midlands' is the wordplay.
'disconnect' becomes 'sever' (I've seen this in another clue).
'midlands' becomes 'n' (I can't explain this - if you can you should give a lot more credence to this answer).
'sever'+'n'='SEVERN'
'from' acts as a link.
Can you help me to learn more?
(Other definitions for severn that I've seen before include "Welsh and English river" , "Britain's longest river" , "Flower" , "Worcester's river" , "River at Worcester" .)