It's too much - put in some water! (5)
I believe the answer is:
steep
'it's too much' is the definition.
(thesaurus)
'put in some water' is the wordplay.
'put' becomes 'tee' (teeing is a kind of putting).
'in' means one lot of letters goes inside another.
'some water' becomes 'sp' (I can't justify this - if you can you should believe this answer much more).
'tee' going into 'sp' is 'STEEP'.
Can you help me to learn more?
(Other definitions for steep that I've seen before include "Hard for cycling" , "Soak thoroughly - precipitous" , "pickle" , "Rapidly rising" , "not reasonable" .)