I accidentally ran across the latest science about the amount of water left underground. Science now thinks that the amount of water underground is as much as in all the oceans, lakes and rivers on the surface of the earth.
There are many sources on this point, including NASA, Northwestern University, etc. Here is just one:
"After decades of searching scientists have discovered that a vast reservoir of water, enough to fill the Earth’s oceans three times over, may be trapped hundreds of miles beneath the surface, potentially transforming our understanding of how the planet was formed."
Earth may have underground 'ocean' three times that on surface