Small amount of water, perhaps (7)
I believe the answer is:
element
This clue is a double definition.
'small amount' is the first definition.
(I've seen this before)
'water perhaps' is the second definition.
(water is a kind of element)
'of' acts as a link.
(Other definitions for element that I've seen before include "piece" , "Primary chemical substance" , "Essential factor" , "Constituent part (7)" , "Eg copper" .)