OnFrom a purely "realistic" stand point, water is the least rare thing in the Belt. There are plenty of asteroids with billions of liters of water, there are dwarf planets spewing out into space. Also that means if there is water, there is O2O2, lots of O2O2. Making water and air an issue in the show and books, showshows no research AT ALL was done on this topic. HaveHaving to travel to Saturn for Water....sigh. It's easy enough to come up with things that could be commodities in a space story. Water and Air and not them.