Just because you cannot figuere out where the water came from for the Great Flood
is not a good enough reason to conclude that it never took place.

In the ancient lore and legend of every culture you will find a story of a disasterous flood. These accounts vary but in distant parts of the world these stories agree on one point. far back in history there was a catacylmsmic flood which wiped out all but a handful of people.
From the indians of north and south america to the Islanders of the Pacific and from the chinese to atleast 40 aborigional races we find the elements of a great flood described.
Geologists of today all over the Earth find a layer of sediment which gives evidence of a worldwide flood.

There are several different theories of where the water might have come from.
Here is the one I have heard:
The Earth had quite a different climate before and after the flood.
for in Geneisis 2:5-6 it states that the lord God had not caused it to rain upon the earth…but there went up a mist from the earth and watered the whole face of the ground.
They argued that Genesis 1:6 described God seperating the waters on the earth from the waters above the Earth. which could describe a canopy of water vapor.Our Earth could have been in effect a giant canopy enclosed garden watered by gentle mists which came out of the ground from the reservoirs of water below the surface.
If the Earth before the flood had been surrounded by a canopy of water vapor above the Troposphere it would have compressed the air beneath and raised the average atmospheric pressure, just how much would depend on how much water the canopy contained.
This increased pressure could have resulted in a greater oxidation rate, a much more efficient metabolism and stronger, healthier people.
The sheilding of water vapor canopy could have eliminated almost all genetic mutation from the harmful solar radiation.
there would be benefits of living under increased atmospheric pressure. During the aquanaut program it was discovered a cut on a aquanauts hand healed completely in 24 hours while submerged in a diving bell.

back then the current land mass was joined together in a hugh continent.
The Earth before the flood was a single land mass riding on a blanket of superheated steam and with an overhead curtain of water vapor protecting it from harmful solar rays.

After the flod the vapor canopy was gone the Earths climate was changed.
Atmospheric pressure dropped to what it is today.
without the water vapor canopy the Earth received more radiation from the sun and genetic mutations occured. mans lifespan was greatly reduced. and they obviosly didnot live as long after the flood.

the other theory that goes with it sometimes is “the fountains of the deep” were also let lose.Gen 7:11 Which combined with the collapse of the water vapor canopy. produced a great amount of water.the ripping apart of the crust would have triggered tsunamis of unparalleled magnitude, sweeping the Earth with walls of water from the existing oceans.
The initial rupture of the earths crust would have spewed a tremendous jet of super heated steam high above the earths ionosphere. the vapor blanket resting on the air above the Earth would have been overwhelmed by the intensity and heat of this supersonic blast and would have collapsed as sheets of worldwide rain.
The jet of water which gushed high above the earths atmosphere would have encountered frigid temperatures converting the water almost instantly to ice crystals.
When the water vapor canopy which covered the Earth up to that point collapsed in rain, ending the green house effect, the temperatures on earth would have been reduced to much the same as they are today. immediately after the flood, the ice crystals formed high above the earths stratosphere would have fallen, dumping immense quantities of ice on the earths polar regions and northern latiitudes. This would explain an enigma which has long perplexed the discovery of animals which had been quick frozen in siberia and alaska some still with undigested food in their stomaches and mouths.
there had to be an abrupt and extremely sudden change in temperature, from near tropical to extreme cold within a matter of minutes.
I kept this in my mind. and a couple of years ago i saw an article in the newspaper where scientists had found a couple miles long of watervapor in the upper atmosphere that was forming over a specific area and they didnt know what it was doing up there. If i find the article i will post it I did cut it out and save it.
nobody knows for sure where the water came from and can only theorize but there was plenty of evidence that it took place. I have read several scientific theories of the water vapor canopy. I could go on and on but i just dont have time. I have several books that mention it. I just pulled a few things out of the books for you to think on.This is just one of several theories I have heard.