Some of the clientele mentioned water, perhaps (7)
I believe the answer is:
element
'water perhaps' is the definition.
(water is one of the four classical elements)
'some of the clientele mentioned' is the wordplay.
'some of' indicates a hidden word.
'ELEMENT' is hidden within 'clientele mentioned'.
(Other definitions for element that I've seen before include "Comfort zone" , "fire, perhaps, once" , "Constituent component" , "Ingredient - small amount" , "Basic chemical unit" .)