Careful and diligent in the use of resources (7)
I believe the answer is:
thrifty
'careful and diligent in the use of resources' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for thrifty that I've seen before include "Careful and diligent in the use of resources" , "Frugal - economical" , "Conserving" , "Sparing" , "Careful with money" .)