Cleaner than bottled water? The science behind astronauts sipping purified urine in space
With no access to resupply missions during extended stays, how astronauts access and recycle water has become a triumph of modern engineering, and a crucial step for future deep space missions.
The question of water in space
As Indian astronaut Shubhanshu Shukla orbits the Earth aboard the International Space Station (ISS) as part of the Axiom-4 mission, one resource is more vital than any other: water. With no access to resupply missions during extended stays, how astronauts access and recycle water has become a triumph of modern engineering, and a crucial step for future deep space missions.
Why water is central to deep space travel
Water plays multiple roles aboard spacecraft, it's not just for quenching thirst. Aside from sustaining astronaut health, it regulates cabin temperature, supports hygiene, and even shields from cosmic radiation. On long missions beyond Earth orbit, resupply from Earth will be impossible, which makes water recycling critical. “The regenerative ECLSS systems become ever more important as we go beyond low Earth orbit,” said Jill Williamson, ECLSS water subsystems manager according to a release by NASA. “The inability of resupply during exploration means we need to be able to reclaim all the resources the crew needs on these missions", he added.
How the ISS turns waste into water
The ISS uses a complex life support system called the Environmental Control and Life Support System (ECLSS), which now recovers up to 98 per cent of onboard wastewater. This includes urine, sweat, cabin humidity, and even used wash water. Christopher Brown from NASA's Johnson Space Center explained, “Let’s say you collect 100 pounds of water on the station. You lose two pounds of that and the other 98 per cent just keeps going around and around. Keeping that running is a pretty awesome achievement.”
The role of the Urine Processor Assembly
At the heart of this system is the Urine Processor Assembly (UPA), which uses vacuum distillation to recover water from urine. The resulting brine, which contains remaining moisture, is processed by the Brine Processor Assembly (BPA). “Before the BPA, our total water recovery was between 93 and 94 per cent overall,” says Williamson. A Brine Processor Assembly (BPA) developed to extract this remaining wastewater has been on the space station as a demonstration of its operation in microgravity.
Extracting every drop
The BPA uses membrane technology and dry air to evaporate the remaining water from urine brine. This humid air, like the moisture from breath and perspiration, is collected by dehumidifiers and sent to the Water Processor Assembly (WPA). The WPA filters the water and purifies it further using a catalytic reactor. It is then tested for purity and, if safe, stored for use, iodine is added to prevent microbial growth.
“Purer than most of the water you drink at home”
Canadian astronaut Chris Hadfield addressed public hesitation in 2013 through a video: “Before you cringe at the thought of drinking your leftover wash water and your leftover urine, keep in mind that the water that we end up with is purer than most of the water that you drink at home,” he said. “That makes the International Space Station its own self-contained environment. That’s a critical step towards living for long periods off of planet Earth.”
Towards sustainable exploration
NASA claims the system now recovers 98 per cent of wastewater, a 3–4 per cent improvement from older systems. Each astronaut uses about a gallon of water per day, making these gains essential for deep space missions. Water recovery is no longer a convenience—it is a necessity for human survival beyond Earth.
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