From a previous post back in Topix days:
What volume of water must be added to the earth to flood all of its land. We do that by comparing the volume of the unflooded earth to the volume of the earth with ocean levels raised to above the highest mountain, Mt. Everest, which stands about five-and-a-half miles high.
[2] The volume of a sphere is =(4/3)(pi)( r^3)
[3] Thus the volume of the unflooded earth is =(4/3)(3.14)(6370) ^3 = 1.08214805 × 10^12 = 1,082,148,050,000 km3
[5] Volume of flooded earth =(4/3)(3.14)(6378. 85)^3 = 1.08666469 × 10^12 = 1,086,664,690,000 km3 [Notice that the radius has been increased from 6370 to 6378.85]
[6] The difference = about 4,500,000,000 km3 of water that must be added to the earth to cover Everest.
[7] “About 3,100 mi3 (12,900 km3) of water, mostly in the form of water vapor, is in the atmosphere at any one time. If it all fell as precipitation at once, the Earth would be covered with only about 1 inch of water.”
http://ga.water.usgs.gov/edu/earthhowmuch.html Thus the atmosphere can provide about 12,900 of the 4,500,000,000 cubic kilometers of water needed, or about 1 inch of the five miles needed. What would happen to the marine life if you added this much fresh water to the oceans?
[8]
The total amount of water on earth is about 1,386,000,000 cubic kilometers http://ga.water.usgs.gov/edu/earthhowmuch.html So, the water needed to flood the land completely - about four times as much water as the earth presently holds in all forms including oceans, ice, lakes, rivers, ground water, atmospheric water, and the water in living things - could neither appear nor disappear without magic, could not be contained in the atmosphere and fall as rain, would fall like a waterfall (30 ft/hr*) everywhere at once destroying the ark and drowning its inhabitants if it did, and **would kill all non-freshwater living aquatic life to boot
*[Forty days is 960 hours. For the water to rise 29029 feet in 960 hours, 30.2 feet of water must fall ever hour over every square inch of the earth at once, or twice as much over half of the earth at once. Imagine a shower filling up a three story building in an hour.]
**[If you added another 4,500,000,000 cubic kilometers of fresh water - in excess of a quadrupling of the total - the salinity of the oceans would fall to about 22.4% of its present level, killing virtually all marine life]