Vichy water (3)
I believe the answer is:
eau
'vichy water' is the definition.
('water' in French - eg in the French town Vichy)
This is the entire clue.
(Other definitions for eau that I've seen before include "Water in France" , "French water, may be Cologne" , "Perrier water" , "French water from chateaux" , "French water - de Cologne?" .)