There is more water under the Seabed than on top of the Seabed. Same as an IceBerg having more ice below the water than on top. These waters are referred to in the Bible as the Fountains of the Deep. These are the waters that came up out of their fountains during Noahs Flood. This is the only possible way that this amount of water could flood all the mountain tops and then disappear within a matter of months.
Most likely a lot of this water is purified.
Praise the Lord!