When did God separate water?

Answer 1

According to Genesis 1, God took a formless void (which apparently already had water) and organized it into the universe. On the second day of creation, he separated the "waters above" from the "waters below." This is a reference to the ancient Israelites' belief that the blue color of the sky was caused by the dome of the earth (they believed that the earth was flat with a dome sky) being surrounded by water. The "waters below" refer to the waters that remained on the earth. On the third day, God organized these waters into oceans, rivers, lakes, etc. This left some of the earth to be dry land.

According to science, God created oxygen isotopes via nuclear reactions in the cores of massive stars. When these stars blew apart, those oxygen atoms combined with the abundant hydrogen atoms within interstellar nebula to form the second most common molecule in the universe (after diatomic hydrogen): H2O.

In the eons of time (illustrating the attribute of God's eternal patience) these molecules coalesced to form icy objects such as comets, some of which impacted the surface of the nascent earth. Thus water came to our planet.

Could comets provide all the water to fill the world's oceans? Easily. Eris is a large cometary body out beyond the orbit of Pluto. It has a volume of 14 billion cubic km. The Pacific Ocean has a volume of 600 million cubic km. In fact, all of earth's oceans are only 1.3 billion cubic km, or 1/10th the total volume of Eris. Of course, Eris is probably only half water ice, the rest of it may be methane, CO2, and other frozen gasses and materials. It's still enough to fill earth's oceans multiple times over.

Answer 2

According to Genesis 1, on the second day.