He perhaps needs part for water heater (7)
I believe the answer is:
element
I believe this clue is a quadruple definition!!
'he perhaps' is the first definition.
(he is a kind of element)
'needs' is a link.
'part' is the second definition.
(element is a kind of part)
'for water' is the third definition.
(thesaurus)
'heater' is the fourth definition.
(thesaurus)
(Other definitions for element that I've seen before include "that's used in heating" , "silver perhaps?" , "Primary chemical substance" , "Constituent -- habitat" , "Basic substance or feature" .)