I recently started watching the TV series "The Expanse", which is based on a series of books (I haven't read). The central premise of the show is that water is a scarce commodity. The Ceres settlement is in fact dependent on shipments of ice harvested in Saturn's rings.
This strikes me as rather odd. Building a closed system which does not waste water at all would seem comparatively easy to me. That would basically solve the entire problem in one swoop.
Building a closed water system would - by my guess - be easier than any of:
- Growing trees on an asteroid
- Building space ships that don't leak any significant amount of air
- Reaching escape velocity regularly
- Building any type of settlement on Mars
- Space warfare
Does the series (either the books or the TV show) offer an explanation why water is such a rare commodity?