If it really rained for forty days and nights, rained enough to cover the world's tallest mountains, that means there would have to have been hundreds of billions of tons of water in order to cover the entire planet.
That means there couldn't be anywhere left for the water to go. Everything would be filled up with water. This means cave systems would have had to have been filled with water too.
So, why isn't there any evidence of a worldwide flood in cave systems such as Mammoth Cave National Park?
And two, where could all the water have gone to?
If it evaporated, how could it have evaporated so quickly?