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If you're reading the KJV, yours says that the windows of heaven were opened up and the fountains of the great deep were broken up (Gen. 8:11).

And it says that the firmament divided the world from the surrounding waters, above and below (Gen. 1:6), and that God put the stars and sun and moon IN the firmament of the heaven (Gen. 1:17).

So, there's earth, in a bubble in the water, with water above and below. And there's "the heaven" the firmament, with the stars set IN it.
And there's God opening the windows of heaven to bring down the flood. Sure it fell as rain. Note that God also opens the stopcocks of the firmament BELOW the earth, and the water wells up from the bubble BELOW too: the great springs were broken open.

Now, it's extrinsic knowledge that the Hebrews actually literally saw the world that way, and we've said "Scripture Alone", but that's what Scripture says. It doesn't just say "it rained". It says that God opened windows in "the heaven", which is says is the firmament, into which it says that the stars are placed. It says that earth is in a bubble. And it tells you that God opened the windows of the bubble to flood the earth.

That is the text.
It doesn't JUST say "it rained".
It says where the rain came from.
It says the rain came through the windows of heaven.
It tells you about the firmament of heaven, which is what was opening.
There's a lot in Genesis.
In fact, but just carefully reading it, you can construct all by yourself the cosmology of the ancient Hebrews (and others). And if you read extrinsic sources, you find out that's exactly what they believed.

Can't limit scripture to the rain. Where the rain came from matters. Where the water welled up from matters. What was outside the firmament and came through the windows of heaven matters.
And that water's still out there, somewhere.