Become depleted (3,3)
I believe the answer is:
run dry
'become depleted' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for run dry that I've seen before include "Exhaust" , "go impassive" , "Come to an end" , "Cease to flow or have any water" , "get exhausted" .)