It's been a rough year for the people who keep the International Space Station (ISS) working. In June, Space X's Falcon 9 rocket disintegrated less than three minutes after launching from Cape Canaveral, Fla., sending a cargo capsule plummeting into the Atlantic Ocean. The failure followed the October 2014 explosion of an Orbital Sciences rocket on a launchpad at the Wallops Flight Facility on Virginia's Eastern Shore. In April, a Russian Progress cargo ship carrying three tons of supplies spun out of control in orbit and was destroyed as it fell back to Earth. 

Both of the U.S. resupply vessels carried water-processing equipment needed on the station. Their failure to reach outer space raised the stakes for the Aug. 19 launch of an unmanned Japanese cargo craft, the Kounotori 5, or White Stork, which successfully docked on Monday. "Once it gets up to the space station, my life gets a whole lot better," says Layne Carter, the water subsystem manager for the ISS at NASA's Marshall Space Flight Center near Huntsville, Ala.

Among the cargo losses on both U.S. launch failures were a pair of multifiltration beds for the water processor and filters for the urine-processing system, which recycles astronauts' waste into a drinking supply. "It tastes like bottled water," Carter says of the water that emanates from the urine processing system, "as long as you can psychologically get past the point that it's recycled urine and condensate that comes out of the air." (Condensate is a polite way of describing the collected breath and sweat of crew members, as well as shower runoff and urine from animals aboard the ISS, including a dozen mice that arrived on the Japanese supply mission.) Without the spares, Carter's team was forced to stop processing condensate for water in mid-July and engineered further ad hoc backup plans to keep the water running in case something went awry. "There's always an adventure right around the corner with the water system," says Carter, a 27-year NASA veteran. 

The space station carries roughly 2,000 liters of water in reserve for emergencies, split about evenly between the U.S. and the Russian sections of the ISS. The two sides operate separate water systems mainly because of decades-old decisions on how best to disinfect water. When the space shuttle program began in 1981, its astronauts' water relied on iodine, a common biocide for water that had long served as a staple for U.S. troops operating in areas with suspect water supplies. Those standard practices carried over to the American side of the space station, which was launched in 1998. It's an effective but inefficient way to clean the water supply, because it has to be filtered out before crew members can drink it. Too much iodine can cause the thyroid gland to become enlarged.

The Russians, however, rely on a different go-to: silver, which in its ionic form is a powerful antimicrobial agent. Its use dates back to the Soviet Mir space station, which was launched in 1986. Unlike iodine, silver doesn't have to be filtered out of the water. Epsom salts are added to improve its taste. NASA has decided to switch to silver-ionized water on future missions, but Carter says he likes that there's both silver- and iodine-treated water aboard the ISS: "It really makes a lot of sense," he says, "to have dissimilar redundancies in the space station in case one of the systems has problems."

The U.S. water recycling system produces about 3.6 gallons per day, for an average of three NASA crew on the ISS, slightly more than the Russians yield from processing just condensate and shower water into a potable supply. The reason? NASA takes Russian urine, too. "We collect it in bags, and then the crew hauls it over to the U.S. side," Carter says. "We don't do 100 percent of the Russian urine. It depends on our time availability."