Regular test to check a water feature (4)
I believe the answer is:
moat
'water feature' is the definition.
'moat' can be an answer for 'water' (I have seen 'Defensive water ' mean 'moat' so perhaps 'water' could also mean 'moat'). I am not certain of the 'feature' bit.
'regular test to check a' is the wordplay.
'regular test' becomes 'mot' (as in an MOT test for a vehicle. I am not sure about the 'regular' bit.).
'to check' indicates putting letters inside (check can mean to restrain or block in).
'mot' enclosing 'a' is 'MOAT'.
Can you help me to learn more?
(Other definitions for moat that I've seen before include "Water round a castle" , "Ditch round castle" , "Water-filled ditch around stronghold" , "Water-filled defensive trench" , "Water crossed via a drawbridge" .)