Biblical Flood: spoiler

Q: How much water is needed to produce the Biblical Flood?

A: 4.5e18 m³.

The Flood covers the mountains by 15 cubits, says Genesis 7:19-20. We assume that the volume of the land is small compared with the volume to be filled (because most of it isn't mountains) so the water is just a spherical shell. The radius of the earth is 6.4e6 m, Everest is 8848m high, and 15 cubits is 6.9m. Hence the amount of water required is
4.5e18 m³ = 4.5e21 kg = 1.5e47 molecules.

The amount of energy required to create this much water (via E = mc²) is 5e38 J.

This much energy would power the sun for 1.3e12 s = 4e4 years.

Non-spoiler