That's an interesting approach. Where did the water come from? Surely they weren't storing it as H20 on the ship? Seems like you'd only want to keep as much as needed for life support in that state. Stored as separate oxygen and hydrogen?
Why not? It's not as if water is flammable, toxic, or highly corrosive - attributes most other fuel sources do have at least one of.
(*Note, I am not an engineer)
Good question! His story "The Martian Way" addresses this. I don't really want to spoil it from you, but basically: where you'd expect.
> Surely they weren't storing it as H20 on the ship?
Why not? It's stable, it's useful for other reasons, and when you've got free energy and easy propulsion, there's no reason not to. (There probably would be some issues with sloshing, actually, but he didn't get into it. Asimov wrote a lot of stories that could be considered Hard Science, but I don't think he'd consider himself an engineer.)