Source regarding series to see in Paris (9)
I believe the answer is:
reservoir
'source' is the definition.
(a reservoir is a supply or source)
'regarding series to see in paris' is the wordplay.
'regarding' becomes 'Re'.
'series' becomes 'ser' (I've seen this in other clues).
'to see in paris' becomes 'voir' (to see in French).
're'+'ser'+'voir'='RESERVOIR'
(Other definitions for reservoir that I've seen before include "Lake used to store water for community use" , "depot" , "Area for storage, of water say" , "water over a wide area?" , "Area flooded" .)