A new comprehensive life-support system for the International Space Station (ISS) centers on a water recycling system whose specially designed filters and chemical processes cleanse waste liquids--notably astronauts' urine and perspiration--so that they become refreshing, drinkable water.

The system, which can produce 2,800 liters of water per year, is fundamentally important because it allows the ISS to house six crew members, up from three, and reduces how much fresh water must be expensively blasted off from Earth inside the Space Shuttle, says Bob Bagdigian, the project manager for the ISS life-support system project, which includes the water recovery system.

"It is a critical part for the next life of the station," says Mary Beth Edeen, manager of the hardware projects office at NASA's Johnson Space Center, in Houston. "It is like a sewage treatment plant and a water treatment plant all in one." Such a system would be a key to future human trips to the moon and, someday, to Mars.

The system was developed at NASA's Marshall Space Flight Center, in Huntsville, AL. It went into orbit in November onboard the Space Shuttle Endeavour and was installed in the U.S. Destiny Laboratory on the ISS. It is currently being tested--samples were collected and returned to Earth on the shuttle for analysis--and is expected to be fully operational by May 2009.

The system is most notable for its ability to turn an astronaut's urine into drinkable water. "Distilling urine in space with the absence of gravity is a significant challenge," says Bagdigian. To compensate for the microgravity environment, the NASA engineers developed a centrifuge-like pretreatment system.

In this system, urine is piped into a rotating drum that spins at high speeds, extracting water vapor, which is then compressed in "a very energy-efficient distillation process," says Bagdigian. The result is what NASA calls a "purified urine distillate," but it's not yet clean enough for astronauts to drink.

This distillate is then combined with the other sources of waste water, including humidity--extracted from the cabin air--that was produced by the perspiration and breath of the astronauts. The combined waste water is put through a particulate filtration and through beds of absorbent materials and other processes similar to those used in commercial, off-the-shelf water treatment systems.