Wants river to flow round between poles (5)
I believe the answer is:
needs
'wants river' is the definition.
'needs' can be an answer for 'wants' ('need' can be a synonym of 'want'). I'm not sure about the 'river' bit.
'flow round between poles' is the wordplay.
'flow round' becomes 'eed' (I am not sure about this - if you are sure you should believe this answer much more).
'between' is an insertion indicator.
'poles' becomes 'NS' (north and south poles).
'eed' put inside 'ns' is 'NEEDS'.
'to' is the link.
Can you help me to learn more?
(Other definitions for needs that I've seen before include "Wants, requires" , "What is required" , "Necessities" , "Calls for" , "shopping-list, say" .)