I remember reading that water is generated as a byproduct of the hydrogen fuel cells on board. And then the water vapour is also recycled and repurified back in

I remember reading that water is generated as a byproduct of the hydrogen fuel cells on board. And then the water vapour is also recycled and repurified back into the system. So it's a closed water system powered by solar energy inputs. Of course, the machinery necessary for this loop costs x billions, but the particular molecules of water used in this experiment probably came out of the internal water cycle and didn't cost to get the water there in the first place.