Drenched with water so he'd have to change (5)
I believe the answer is:
hosed
'drenched' is the definition.
(I've seen this in another clue)
'so he'd have to change' is the wordplay.
'have to change' indicates anagramming the letters (I've seen 'has to change' mean this).
'so'+'hed'='sohed'
'sohed' is an anagram of 'HOSED'.
'with water' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for hosed that I've seen before include "Watered with a flexible pipe" , "washed" , "wearing tights?" , "swilled down with water" .)