[LandStander]

Water mined from the moon might be much cheaper by the time something like this is built. That being said, a giant sterile swimming pool seems like an odd feature for an interplanetary spacecraft. I'd rather see a well-balanced aquatic habitat, if anything.

[m4rtink]

It could very well double as emergency reaction mass/ring weight trim/liquid radiation shielding/source of drinkable water and oxygen. :)

[hwc]

or capture a small comet!