Weapon religious group deployed round a water source (8)
I believe the answer is:
catapult
'weapon' is the definition.
(I've seen this before)
'religious group deployed round a water source' is the wordplay.
'religious group' becomes 'cult' (I've seen this before).
'deployed round' indicates putting letters inside.
'water source' becomes 'tap'.
'a'+'tap'='atap'
'cult' going around 'atap' is 'CATAPULT'.
(Other definitions for catapult that I've seen before include "Weapon projecting stones" , "Weapon of ancient wars" , "Launch" , "Weapon for hurling stones" , "Throwing device or sling" .)