Croatians regularly shower (4)
I believe the answer is:
rain
'shower' is the definition.
('rain shower' can be a synonym of 'shower')
'croatians regularly' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternate letters of 'croatians' are 'RAIN'.
(Other definitions for rain that I've seen before include "Precipitation" , "Wet weather" , "Fall wetly" , "Falling water" , "Storm" .)