for the LORD God had not caused it to rain upon the earth, and there was not a man to till the ground.
This is after the 7th day of rest that the earth was 'watered' without rain. So all that water of Genesis 1:2 had to go someplace.
In Genesis 1:7 God divides the waters and creates the firmament, which should not be confused with the common notion of "firm ground". The firmament, ( See Webster's ) means "The vault or arch of the sky," and it created a protective enclosure within the waters of chaos.