Salt water, perhaps, destroyed aliens (6)
I believe the answer is:
saline
'salt water' is the definition.
(I know that saline is a type of salt water)
'destroyed aliens' is the wordplay.
'destroyed' indicates an anagram.
'aliens' with letters rearranged gives 'SALINE'.
'perhaps' is the link.
(Other definitions for saline that I've seen before include "Containing salt for aliens" , "Like contents of cellar" , "Containing salt or salts" , "Intravenous feeding" , "Salty to aliens" .)