Spooner's happy supporter works on water (8)
I believe the answer is:
ferryman
'works on water' is the definition.
(someone who works on water)
I can't explain the rest of the clue.
(Other definitions for ferryman that I've seen before include "Transporter across water" , "Aquatic taxi driver" , "One plying a short water crossing" , "eg Charon (on the Styx)" , "Charon's occupation on the River Styx" .)