Living in water (7)
I believe the answer is:
aquatic
'living in water' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for aquatic that I've seen before include "Of the water, its animals, its sports" , "Relating to water" , "Marine - living in water" , "20 [TERRAPIN] is" , "Growing in or near water" .)