Keeping alien in wet conditions (9)
I believe the answer is:
retaining
'keeping' is the definition.
(retaining is a kind of keeping)
'alien in wet conditions' is the wordplay.
'alien' becomes 'et' (extra terrestrial).
'in' means one lot of letters goes inside another.
'wet conditions' becomes 'raining' (I can't justify this - if you can you should give a lot more credence to this answer).
'et' placed within 'raining' is 'RETAINING'.
Can you help me to learn more?
(Other definitions for retaining that I've seen before include "Hanging on to" , "Holding back in Tangier" .)