An ocean would be difficult to justify, but a *frozen* ocean could be workable. One could, presumably, also posit the existence of subsurface "icebergs" left by impact. In reality, any impactor is likely to be blown not to bits but to vapor, but with the assumption of 19th century scientifiction, perhaps such impactors just bury themselves under the craters they make. Which could lead to story possibilities... each crater has a different nugget underneath. This one water, that one iron, that one carbon, with mining operations on various ones with an economy forming based on trade between facilities. And with theft/piracy and such, fighting over more valuable mines.
Perhaps nobody knows *what* nugget is under a crater until the drill team gets there. Most craters in fact have no nugget; perhaps only one in a hundred or a thousand, the bulk having been properly vaporized. A scene with a drill team devastated when they find that after many dry holes they finally get one with a nugget... and its economically unviable silver. And they are crushed when they hear over the radio that their arch-nemesis competing drill team just struck it rich with a rich seam of water.