Once the water is purified, astronauts will do everything possible to use it efficiently. "On the ground, people flick on the faucet and they probably waste a couple of liters of water just because it's free and the water pressure is high," notes Carter.

"On the ISS, the water pressure will be about half what you might experience in a typical household," Carter said. "We don't use faucets on the ISS, we use a wash cloth. It's much more efficient. If you're an astronaut, you'll wet the wash cloth with a spray nozzle and then use the cloth to wash your hands.On the space station, people will wash their hands with less than one-tenth the water that people typically use on Earth. Instead of consuming 50 liters to take a shower, which is typical on Earth, denizens of the ISS will use less than 4 liters to bathe.

Even with intense conservation and recycling efforts, the Space Station will gradually lose water because of inefficiencies in the life support system.

"We will always need resupply, because none of the water reprocessing technology that is available right now for space flight ... is 100 percent efficient. So there's always some minimal loss," said Marybeth Edeen, deputy assistant manager of environmental control and life support at NASA's Johnson Space Center.

Water is lost by the Space Station in several ways: the water recycling systems produce a small amount of unusable brine; the oxygen-generating system consumes water; air that's lost in the air locks takes humidity with it; and the CO2 removal systems leach some water out of the air, to name a few.

Lost water will be replaced by carrying it over from the Shuttle or from the Russian Progress rocket. The Shuttle produces water as its fuel cells combine hydrogen and oxygen to create electricity, and the Progress rocket can be outfitted to carry large containers of water.

NASA scientists will continue to look for ways to improve the life support systems of the Space Station, reducing water losses and finding ways to reuse other waste products. If the water recycling systems can be improved to an efficiency of greater than about 95 percent, then the water contained in the Station's food supply would be enough to replace the lost water, Edeen said. "It takes processes that are slightly more efficient than we have developed for the space station to do that," Edeen said.

"Those are the next generation water processing systems. Those are being developed now, but they're not ready for space flight yet." The ECLSS life support system will join the Space Station as part of Node 3, which is scheduled to launch in October 2005. Until then, the environment inside the ISS will be maintained primarily by life support systems on the Russian Zvezda Service Module. "