When I was young, the WT society supported (a little green book) the "water-canopy theory", a version where the water needed for the flood had been in the atmosphere. I wonder if they have cancelled that teaching or just decided to forget it.
It was argued that high enough in the atmosphere there are conditions suitable for water to exist in vapor phase. One of my first enlightments concerning the authority of the WT was related to this argument. First, if you add so much water in the atmosphere, it is no more the same atmosphere, so there is no point in referring to the conditions now. Second, related, if there were enough vapor to correspond to, say, one kilometer deep layer of liquid water on the surface of the earth, that would make the air pressure down here a hundred times larger.