NASA's plans to continue its exploration of the solar system do not include packing enough drinking water for astronauts during months-long missions. Instead, NASA will rely on a water-recovery system that recycles not only condensed water vapor and trace contaminants from crew perspiration and respiration but urine as well.

Such technology has been in development for decades. But the water-recovery system that will become part of NASA's Regenerative Environmental Control and Life Support System, or ECLSS, for the International Space Station (ISS), still needs a number of improvements if it is to support the space agency's ambitions of returning to the moon and pushing onward toward Mars. Logistics aside, it costs about $5,000 per kilogram (2.2 pounds) to ship water in a space shuttle. The costs on longer missions are likely to be higher.

For the purposes of spaceflight or a space station, a water-recovery system collects urine from the astronauts and condensation from the cabin air and, through a series of chemical treatments and filters, turns that moisture into drinkable water. The first step involves filtering solid particles such as skin cells and hair out of the liquid. After that, contaminants are chemically dissolved and oxygen is added to the liquid to oxidize trace organics so that they, too, can be removed. Next, the liquid is "polished," meaning chemicals left over from the cleaning process are removed. Finally, iodine is added for microbial control, much the way municipal water authorities add chlorine to city drinking water. The resulting liquid is sent to a large storage tank, which can be tapped for drinking.

At this point, the water-recovery systems NASA is developing are capable of capturing up to 85 percent of the water in urine. Including the purified condensation, NASA scientists are able to retrieve 92 percent of waste moisture produced during a space mission.

But the water-recovery systems will have to do much better if they are to travel with astronauts to the moon or Mars. "Recovering 92 percent of the water is great, and that is a sustainable amount of water recovery in low Earth orbit," says Bob Bagdigian, project manager for the ECLSS Center at NASA's Marshall Space Flight Center in Huntsville, Ala. "But that missing 8 percent becomes a difficult amount to bear on longer missions."

There are three water-recovery systems under development. In addition to the Marshall device, others are being tested at NASA's Ames Research Center at Moffett Field, Calif., and Johnson Space Center in Houston. The finished product, likely featuring the best parts taken from all three, will consolidate some of the processes that are done separately today. Instead of initially processing urine and condensation separately, the finished recovery system may collect urine and condensation together, plus any water remaining from laundry or showers. (Whereas there are currently no clothes washers or showers on the ISS, NASA does not rule them out for exploratory missions.) Diluting the urine up front makes the decontamination process more efficient.

Changes in the types of chemicals that astronauts use on board a spacecraft can help make water retrieval more efficient. "You'll have to use a soap that you won't have a hard time removing from the water," says Monsi Roman, a Marshall microbiologist and project manager for life support on exploration missions, such as those to the moon and Mars.

The water-recovery system, set to be delivered to the ISS on a September 2008 shuttle mission, will be self-contained, which means the astronauts will not have to manually initiate the various steps required to make drinking water, Roman says. Still, the system has a lot of components and many of them will have to be replaced periodically. "For every 100 kilograms [(220 pounds)] of water that the system produces, you have to replace eight kilograms [(17.5 pounds)] worth of equipment," Bagdigian says. "We need to reduce this rate while increasing the water recovery rate."

As early as the late '60s and early '70s, "we knew that exploration away from the earth was going to require the recycling of water and oxygen," Bagdigian says. Russian cosmonauts have been collecting and recycling moisture out of cabin air systems since the Salyut 1 and Mir space stations, which launched in 1971 and 1986, respectively. The Russians also did some work developing electrolyzers that can convert water, via electrolysis, into gaseous hydrogen and oxygen. "They've incorporated these technologies into their side of the [International] Space Station," he says.

While none of this conjures up thirst-quenching images of cold, clear water flowing down a mountain stream, NASA did conduct some blind taste tests that compared the recycled drinking water with plain tap water as well as with tap water that had iodine added to it. On a scale of one to nine, none of the waters scored higher than five. The most typical reaction after drinking the recycled water was to notice the taste of the iodine. The version of the water-recovery system that will be installed on the ISS next year will feature an added step that scrubs the iodine out of the finished product.

In the end, the goal is to simulate the way nature recycles urine and other human by-products. "The difference is," Roman says, "in a station on the moon, you'll know whose urine you're drinking."