Home Counties spirit, a watery liquid! (5)
I believe the answer is:
serum
'a watery liquid' is the definition.
(I've seen this before)
'home counties spirit' is the wordplay.
'home counties' becomes 'se'.
'spirit' becomes 'rum' (I've seen this before).
'se'+'rum'='SERUM'
(Other definitions for serum that I've seen before include "Antitoxin derived from blood" , "Inoculation liquid" , "Part of blood; vaccine" , "Liquid separating from coagulating blood" , "Antidote" .)