Net adjustment by water board (7)
I believe the answer is:
entrain
'board' is the definition.
(I know that entrain is a more specific form of the action board)
'net adjustment by water' is the wordplay.
'adjustment' indicates an anagram (the order of letters is adjusted).
'by' means one lot of letters go next to another.
'water' becomes 'rain' (rain is a kind of water).
'net' with letters rearranged gives 'ent'.
'ent'+'rain'='ENTRAIN'
(Other definitions for entrain that I've seen before include "board the Orient Express?" , "Sweep along" , "Bring about as consequence" , "Go on board at the station" , "Board a rail service" .)