When astronauts travel into space, they carry along air and water. Volume and weight restrictions limit the amount of supplies that can be carried, so water must be rationed and recycled. This is especially important on long missions. Extended stays at the International Space Station would not be possible without careful recycling.
Water recycling has always been employed at the space station. It is not a glamorous aspect of being an ISS crew member, but astronauts must even recycle urine to preserve limited drinking water supplies.
Recycling equipment on the ISS is a system of modular components. A separate water processor assembly and urine processor assembly function together as the water recovery system, and the water recovery system is part of the larger oxygen generation system. These systems function together to produce enough air and water to support seven ISS crewmembers for extended stays in space.
If manned space exploration is to progress further, size and efficiency of recycling equipment must be optimized. Preservation of all available resources will be critical to interplanetary travel to Mars or the establishment of a lunar colony. The technology ultimately used must be able to sustain astronauts for a period of three years without external resupply.
Researchers are working steadily on several different approaches to recycling. Some efforts focus on mechanical processing, while others use chemical reactions to reclaim oxygen and water. Some research even focuses on bacterial processes, similar to those used at wastewater treatment facilities on Earth, to produce air and drinking water.