Well that relates to something I heard a few years ago about there being more water in the earth's crust and mantle than in the oceans. Isn't there some SciFi book along those lines with the water rising up? Not something I've actually read, but I'm pretty sure I heard about it.

The water exists in the rock mostly like water exists in the silica packets in everything you buy these days -- chemically bound in hydrated forms of crystals. That means it must be taken into account in any chemistry models, but not that there's a giant reservoir underground waiting to burst out in a flood.