Depends on if the kid meant "in space" or "on something like the space station".
Kids being kids, he probably literally meant space, not realizing the implications of water (possibly) becoming gaseous from lack of pressure (I assume?).
For that age, it would be a good learning experience to explain in a spaceship vs in space - just not the triple point of water, or the different ices, etc.
You buy as much space as you'll need in the next few years and make a plan for proper duplication/backup, such as 3-2-1 Backups.