I'm working on a science fiction short story and was wondering if there were any liquids that would be safe to bathe in while traveling on a space craft with artificial (spin-based) gravity. In such a context hydrogen and oxygen are valuable resources not to be wasted. While bath water could be recycled, it is not available for other uses while someone is sitting in it, so I was wondering if there are other liquids at Standard Temperature Pressure that would be safe to bathe in (potentially ingesting small amounts).
I thought of using carbon bucky-ball fullerenes in a fluid but the viscosity looks to be much too high (essentially tar-like). I know there are waterless chemicals that can be used for cleaning (e.g. DryBath), the purpose of this is more to have a hot-tub to relax in than to disinfect and clean. If the addition of some hydrogen and oxygen (either as H2O or in other compounds) can improve the viscosity or is necessary to form the liquid, that is acceptable as long as less than 10% of the liquid is comprised of hydrogen and oxygen. The purpose is to save water and oxygen for air while still being able to soak in a hot-tub.
Unfortunately most oils contain a substantial amount of hydrogen and some oxygen, so they don't qualify unless the amount of carbon offers substantial savings in volume. I'd prefer something without any hydrogen or oxygen if such a chemical exists.
This is my first post here and I'm unfamiliar with the tags, so feel free to edit or add any you feel are appropriate.