Student requiring support to install shower (7)
I believe the answer is:
trainee
'student' is the definition.
(I've seen this before)
'support to install shower' is the wordplay.
'support' becomes 'tee' (tee is a kind of support).
'to install' means one lot of letters goes inside another.
'shower' becomes 'rain' (synonyms).
'tee' enclosing 'rain' is 'TRAINEE'.
'requiring' acts as a link.
(Other definitions for trainee that I've seen before include "novice" , "A beginner in Aintree" , "One being taught a job" , "One taking instruction" , "one not yet qualified" .)