After-effect of rain in Italy -- letting in water maybe (6)

I believe the answer is:

porose

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'after-effect of rain in italy letting' is the definition.
I can't tell whether this definition defines the answer.

'water maybe' is the wordplay.
'water' becomes 'po' (Po is an example).
'maybe' becomes 'rose' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'po'+'rose'='POROSE'

'in' is the link.

Can you help me to learn more?

I've seen this clue in The Telegraph.

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