Where could the waters possibly exist if there are no heavens or earth? If there was no place for water to exist then one would have to conclude that the waters had to have been created after the heavens and the earth.
The waters do not need to be above the earth or below the heavens to exist. So I'm not sure what you mean. And I'll repeat, Genesis describes the creation of things that are already there (giving form to that which was formless and filling that which was empty).
If I said, "in the beginning when I created a boat, the boat was broken and empty, and darkness was on the face of the deep, and a bird flew over the waters, then I said "someone pass me a hammer"".
And in 6 hours I created the boat, I put my passengers in it (Adam and Eve) and I said, that's very good. It now has form and it's filled with people.
You wouldn't turn and say "well how can waters be there if there is no boat? If there is no place for the waters to exist, then one would have to conclude that the waters had to have been created after the boat"
That doesn't make any sense. The waters are above the heavens and below the earth. They are of a further extent than these spaces.
To him who spread out the earth above the waters, for his loyal love endures forever.
Psalms 136:6
Praise him, highest heavens, and waters above the heavens. Let them praise the name of Yahweh, because he commanded and they were created. And he put them in place forever and ever, by a decree he gave that will not pass away.
Psalms 148:4-6
That's why Genesis even says,
Genesis 1:7-8 ESV
[7] And God made the expanse and separated the waters that were under the expanse from the waters that were above the expanse. And it was so. [8] And God called the expanse Heaven. And there was evening and there was morning, the second day.
The heavens themselves are in the midst of the waters. The waters are not in the midst of the heavens.
Genesis 1:9 ESV
[9] And God said, “Let the waters under the heavens be gathered together into one place, and let the dry land appear.” And it was so.
The waters below the heavens were gathered into one place, revealing the earth in the midst of the waters. The primordial mount, almost like an island.
Genesis 1:10 NASB1995
[10] God called the dry land earth, and the gathering of the waters He called seas; and God saw that it was good.
And the waters that were gathered into 1 place, were called "seas". That is, seas that surround the primordial mound.
So you see, the heavens and the earth are both in the midst of the waters. The waters are not in the midst of the heavens and the earth (at least not in totality).
And all this is of course subject to debate because the Bible shifts cosmological positions depending on what book of the Bible you're in. Like others are saying, it's not something to think about scientifically. It's more phenomenological and literary.