From the King James Bible
God said, "Let there be a firmament in the midst of the waters, and let it divide the waters from the waters. And God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament: and it was so. And God called the firmament Heaven. And the evening and the morning were the second day.
Whether the firmament was considered to be made up of a solid material, or was simply an expanse, it is clear that the ancients thought that there was a body of water ABOVE heaven.
Where does water appear to come from when it rains? Heaven. Thus the "Waters above the Firmament" was simply the ancient Jewish explanation for the source of the water when it rains.
This is so clear I do see why anything could be said against this understanding.
Except it is unacceptable to those who believe that the Bible is the word of God, because there are NO waters above the heavens (the firmament)! And so they have a problem!