Apsû

The apsû (also known as abzu or engur) was the name for the mythological underground freshwater ocean in Sumerian and Akkadian mythology.  Lakes, springs, rivers, wells, and other sources of fresh water were thought to draw their water from the apsû.The Sumerian god Enki (Ea in the Akkadian language) was believed to have lived in the apsû since before human beings were created. His wife Damgalnuna, his mother Nammu, his advisor Isimud and a variety of subservient creatures, such as the gatekeeper Lahmu, also lived in the apsû.In the city Eridu, Enki's temple was known as E-abzu ("the abzu temple") and was located at the edge of a swamp, an apsû.
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Noun
1. father of the gods and consort of Tiamat
(hypernym) Semitic deity
(classification) Mesopotamia

[Mesopotamian] A primeval Sumero-Akkadian god who personifies the primordial abyss of sweet waters underneath the earth. He is the consort of Tiamat, the primordial abyss of salt waters of Chaos. In the later mythology of the Enuma Elish, the sweet water mingled with the bitter waters of the sea and with a third watery element, perhaps cloud, the first gods were engendered. The waters of Apsu were thought of as held immobile underground by the 'spell' of Ea in a death-like sleep, but it is also said that Ea had Apsu fallen asleep and had killed him. From the clay of Apsu man was fashioned. This appears to be a Sumerian myth, because in the Enuma Elish, Kingu's blood serves this purpose. Apsu's vizir, Mummu, was imprisioned in a house built on his body.

Apsu (Babylonian) Abzu (Sumerian) Also Ab Soo. The primordial deep; the waters of space in the Babylonian epic of creation Enuma Elish (when on high). From Apsu and Tiamat were born all the gods, man being fashioned from the clay of Apsu in a Sumerian version, and from the blood of Kingu, son and second consort of Tiamat, in Enuma Elish. The deep is the abode of Ea (wisdom) who saves humanity from destruction by Apsu, Apsu being transformed into still or stagnant subterranean waters.
The Babylonian hero-creator is Marduk, whose prowess against the monstrous forces of Tiamat (matter) caused the gods to endow him with the power to overcome them and to complete the creation of heaven and earth.