Thread: Water And Oxygen on the ISS

I'm posting here because I wasn't sure what category this would fit in, so here's my question:

I read that water on the ISS is recycled, every last drop of it, down to the condensing of breath, which continuously supplies the astronauts with potable water.
That's fine.
But I also read that the main source of oxygen was from the electrolysis of water into hydrogen and oxygen, with the oxygen vented into the cabin and the hydrogen vented externally.
How on earth (or rather, off of earth) are they recycling water that gets split, then half inhaled and the other half ejected into space?

Originally Posted by Jason Summer

How on earth (or rather, off of earth) are they recycling water that gets split, then half inhaled and the other half ejected into space?

They replace the lost water with water hauled up from Earth.

Right now they use a sorbent bed to absorb CO2, then they purge the CO2 in the bed out into space. It's easy and almost foolproof.

The "holy grail" is a system that uses electrical energy to split CO2 back to carbon and oxygen - then you just dump the carbon overboard. There's currently no easy way to do that. However, a system that gets halfway there is a recently developed system that uses catalysts to crack CO2 into CO (carbon monoxide) and oxygen. Recycle the oxygen and vent the CO, and you only have to haul half as much water to the ISS.

Wow. Sounds expensive. How often are water rockets sent there, and how much oxygen can you get out of it?