The question that seems to be keeping all of you awake at night these days seems to be:
The Bible says that the entire earth was covered with water. If that is true, then where did all the water come from, and where did it go after the flood?
In order to answer the question, we have to look at the pre-flood atmospheric conditions. First of all, we know that there was no rain until the flood occurred. Instead of rain, the earth had a heavy mist encircling the globe, which kept everything lush and green (which is why we always picture dinosaurs in a jungle-like, lush environment--the world was much more beautiful back then because it was fresh from creation!).
Second, the world didn't have huge mountains like we have today (since modern mountains and mountain ranges were formed by volcanic activity and sedimentary rocks. This is a vital point, because if the mountains back then weren't as high as they are now, then it wouldn't have taken an impossible amount of water to cover them! As it is, if we took all the water in the oceans today we could cover the whole earth (were it smooth) quite a ways (I can't recall the exact number, but it was at least seven thousand feet).
Since there was no rain before the flood (and yet there *were* rivers), it makes plain sense that there were underground reservoirs of water which fed springs. When these underwater lakes were broken, there would have been a lot of water geysering out of the ground.
Then, the rain would have been supplied by the large moisture density which covered the earth: The catastrophic hypercanes and other weather factors would have caused all that moisture to form water droplets which would have torrented to the earth.
The oceans were likely much warmer back in the pre-flood days, which would have created ideal conditions for gigantic hypercanes and other disasters. Couple with that earthquakes and volcanic eruptions, overflowing rivers and geysers, huge torrents of water sheeting from the skies, giant tsunamis destroying the civilized world --havoc reigned.
People have gotten into their heads that the flood was just a calm little pond that washed over the earth, with Noah and all the animals sticking their heads out of a little houseboat. But this is not what really happened. For one, a houseboat would not have fit all the animals. ;) We can see the measurements for the Ark in Genesis 6:15-16, and it was no pleasure yacht. The Since God commanded two/seven of every kind of animal, (kind meaning species, as in Genesis 1:25), then there wouldn't have been that many. There is a hypotheses that the Lord put the animals into a sort of hibernation so that they wouldn't require much food or water or anything.*shrug*
Again, what is given as evidence against the flood, when we take all factors into account, actually support the Flood of the Bible.