Albert Barnes Commentary Jeremiah 2:13

"For my people have committed two evils: they have forsaken me, the fountain of living waters, and hewed them out cisterns, broken cisterns, that can hold no water." — Jeremiah 2:13 (ASV)

Pagans are guilty of only one sin—idolatry; the covenant-people commit two: they abandon the true God; they serve idols.

Fountain—Not a spring or natural fountain, but a tank or reservoir dug in the ground , and primarily intended for storing living waters, that is, those of springs and rivulets. The cistern was used for storing up rainwater only, and therefore the quantity it contained was limited.