Unwanted discharge of fluid (7)
I believe the answer is:
leakage
'unwanted discharge of fluid' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for leakage that I've seen before include "Percolation" , "Accidental spill" , "Liquid/gas accidentally lost" , "Escape of liquid or gas - or confidential information" , "Accidental escape (of a liquid or gas)" .)