Due to some counterintuitive geothermal reasons, it's likely that three of the four Galilean moons (of Jupiter) as well as Titan (Saturn's largest moon) all sport significant underground oceans of liquid water.
For example, despite being much smaller than the Earth, Ganymede is projected to harbor more liquid water than all of Earth's oceans combined.
(Whether this adds up to 30% depends heavily on what you start counting as a "body")
For example, despite being much smaller than the Earth, Ganymede is projected to harbor more liquid water than all of Earth's oceans combined.
(Whether this adds up to 30% depends heavily on what you start counting as a "body")