Water ultimately coming in pipe for Arab? (5)
I believe the answer is:
horse
'arab?' is the definition.
(arab is a kind of horse)
'water ultimately coming in pipe' is the wordplay.
'ultimately' says to take the final letters.
'coming in' indicates putting letters inside.
'pipe' becomes 'hose' (I've seen this before).
The final letter of 'water' is 'r'.
'r' placed into 'hose' is 'HORSE'.
'for' acts as a link.
(Other definitions for horse that I've seen before include "Vaulting --; -- sense" , "Might one be up on this" , "Domesticated animal" , "animal in the gym" , "what has croup in the end?" .)