Subterranean waters
Defined in 1 dictionary — Black's (1910)
Black's Law Dictionary
Henry Campbell Black, M.A. · 1910
Waters which lie wholly beneath the surface of the ground, and which either ooze and seep through the subsurface strata without pursuing any defined course or channel, (percolating waters.) or flow in a permanent and regular but invisible course, or lie under the earth in a more or less immovable body, as a subterranean lake.
Defined under Water in Black's Law Dictionary.