Patch of water returns to the pit - way of escape needed (8)
I believe the answer is:
loophole
'way of escape needed' is the definition.
I can't judge whether this defines the answer.
'patch of water returns to the pit' is the wordplay.
'patch of water returns' becomes 'loop' (I can't justify this - if you can you should give a lot more credence to this answer).
'to the pit' becomes 'hole' (a pit is a hole).
'loop'+'hole'='LOOPHOLE'
Can you help me to learn more?
(Other definitions for loophole that I've seen before include "Way of evading a rule or contract" , "opening" , "Flaw or ambiguity in a rule" , "useful for defence" , "Opportunity to evade difficulty" .)