“…the name for fresh water from underground aquifers which was given a religious fertilising quality in Sumerian and Akkadian mythology. Lakes, springs, rivers, wells, and other sources of fresh water were thought to draw their water from the abzu. In this respect, in Sumerian and Akkadian mythology it referred to the primeval sea below the void space of the underworld (Kur) and the earth (Ma) above.”

Source: Abzu – Wikipedia