There might be aquifers below the surface of rocky bodies, provided sufficient heat and pressure exist to keep the water liquid. But this would be water in crac

There might be aquifers below the surface of rocky bodies, provided sufficient heat and pressure exist to keep the water liquid. But this would be water in cracks on the rock, or in between grains of sand if sedimentary rocks exist. However, Europa is thought to have actual liquid oceans; these are underneath the ice that is the outer surface of the planet. It is unlikely for there to be a water layer under rock because it would be gravitationally unstable to have a low-density layer under a higher one.