Turned source of water green (5)
I believe the answer is:
olive
'water green' is the definition.
'olive' can be an answer for 'green' (olive green is a kind of green). I'm not certain of the 'water' bit.
'turned source of' is the wordplay.
'turned' is a reversal indicator.
'source' becomes 'evil' (I have seen 'source of harm' mean 'evil' so perhaps 'source' could also mean 'evil').
'of' becomes 'o''.
'evil'+'o'='evilo'
'evilo' in reverse letter order is 'OLIVE'.
Can you help me to learn more?
(Other definitions for olive that I've seen before include "Small green tree-fruit, nice in martini" , "Fruit giving oil" , "A Med. fruit-tree" , "This branch is offered in peace gesture" , "Oil-yielding tree" .)