Rod's called out in hellish water (4)
I believe the answer is:
styx
'hellish water' is the definition.
(mythical river on way to hell)
'rod's called out' is the wordplay.
'rod's' becomes 'stick's'.
'called out' shows a homophone (sound like).
'sticks' is a homophone of 'STYX'.
'in' is the link.
(Other definitions for styx that I've seen before include "Underworld river; sounds like remote area" , "River around Hades" , "Infernal runner" , "One of the underworld rivers" , "Underworld river ferried by Charon" .)