Louche fauns regularly seen in water (5)
I believe the answer is:
ocean
'water' is the definition.
(ocean is a kind of water)
'louche fauns regularly seen' is the wordplay.
'regularly seen' means one should take alternating letters.
'louche'+'fauns'='louchefauns'
The alternating letters of 'louchefauns' are 'OCEAN'.
'in' acts as a link.
(Other definitions for ocean that I've seen before include "Large amount of water and" , "Large stretch of water" , "One of the Seven Seas" , "Large expanse of water" , "Huge expanse" .)