By the sound of it, drops of water on grass expected (3)
I believe the answer is:
due
'expected' is the definition.
(I've seen this before)
'by the sound of it drops of water on grass' is the wordplay.
'by the sound of it' indicates a 'sounds like' (homophone) clue.
'drops of water on grass' becomes 'dew'.
'dew' sounds like 'DUE'.
(Other definitions for due that I've seen before include "Expected; proper" , "Scheduled to arrive" , "Outstanding" , "Ripe for payment or arrival" , "Rightful" .)