run low
To near the end of a supply of something. We're running low on paper towels right now, so use them judiciously.
run low (on something)
to near the end of a supply of something. We are running low on salt. It's time to buy more. The car is running low on gas.
be/run ˈlow (on something)
not have much of something left: We’re running low on fuel. Do you think we’ll have enough to get home?