Dwindle, dry up (7)
I believe the answer is:
shrivel
I believe this is a double definition.
'dwindle' is the first definition.
(I've seen this in another clue)
'dry up' is the second definition.
(thesaurus)
(Other definitions for shrivel that I've seen before include "Wither from lack of water" , "Contract into wrinkles" , "Wither with loss of moisture" , "Desiccate" , "Wither, shrink" .)