Said to be in power shower (4)
I believe the answer is:
rain
'shower' is the definition.
(rainfall)
'said to be in power' is the wordplay.
'said' shows a homophone (sound like).
'to be in power' becomes 'reign' (I've seen this in another clue).
'reign' sounds like 'RAIN'.
(Other definitions for rain that I've seen before include "Fall in large quantities" , "See 12" , "downfall?" , "bad weather" , "Falling water" .)