Green water often bottled up (5)
I believe the answer is:
naive
'green' is the definition.
('naive' can be similar in meaning to 'green')
'water often bottled up' is the wordplay.
'water often bottled' becomes 'evian'.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'evian' written backwards gives 'NAIVE'.
(Other definitions for naive that I've seen before include "Lacking guile" , "Short on experience" , "Ingenuous and credulous" , "Artless, innocent" , "Simple and guileless" .)