Silly exploit with plant that flavours water (7-5)

'silly' is the definition.

'exploit with plant that flavours water' is the wordplay.
I cannot really understand how this works, but
'exploit' could be 'feat' (synonyms) and 'feat' is present in the answer.
'plant' could be 'herb' (herb is a kind of plant) and 'herb' is found in the answer.
'water' could be 'rain' (rain is a kind of water) and 'rain' is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?