On the International Space Station, astronauts don’t just drink water-they drink urine. Not the kind you’re thinking of. They drink water that was once sweat, breath, and urine, cleaned so thoroughly it’s safer than most tap water on Earth. This isn’t science fiction. It’s the reality of living in space for months or years. And it’s the only way humans can survive long missions to the Moon, Mars, or beyond.

Why Water Recycling Isn’t Optional in Space

Sending water to space costs about $22,000 per liter. That’s not a typo. For a six-person crew on a 180-day mission, you’d need over 3,000 liters of water just for drinking, hygiene, and food prep. That’s more than $66 million in transport costs alone. And that’s before you even think about a Mars mission, which could last three years. Resupply missions aren’t feasible. You can’t wait months for a cargo ship to arrive if your water runs out.

That’s why NASA built a system that turns waste into water. Not just a little. Not 70%. Not 80%. 98%. That’s the target. And on the ISS, they’ve hit it.

How the ISS Water Recovery System Works

The Water Recovery System (WRS) on the ISS isn’t one machine. It’s two main systems working together: the Urine Processor Assembly (UPA) and the Water Processor Assembly (WPA). Together, they handle everything from sweat on the walls to bathroom flushes.

The UPA starts the process. It spins urine at 30,000 revolutions per minute in a vacuum, heating it to 80-90°C. This boils off the water while leaving behind salts and urea. It pulls out about 75% of the water from urine. The rest becomes a thick, salty brine-until 2022, when NASA added the Brine Processor Assembly (BPA). That new unit pulls another 10-15% of water from that leftover sludge using warm, dry air and special membranes. Now, nearly every drop counts.

That water, along with sweat and humidity from the air, moves to the WPA. Here, it goes through six stages:

1. Two filters remove particles down to 1 micron-smaller than a bacterium.
2. Activated carbon and ion-exchange resins soak up chemicals and odors.
3. A catalytic reactor heats the water to 130°C with oxygen, breaking down organic waste into harmless bits.
4. More ion-exchange polishing removes leftover ions.
5. Iodine is added to kill any lingering microbes.
6. Final sensors check conductivity and organic content to make sure it’s clean.

The result? Water that meets or beats U.S. Environmental Protection Agency standards. In fact, astronauts say it tastes better than the water they had on Earth before training.

What Makes This System So Different from Earth

On Earth, water treatment plants use bacteria, gravity, and large tanks. Space doesn’t have any of that. No gravity means liquids don’t settle. No room means every liter of equipment has to be compact. And the waste? It’s worse than sewage.

Astronaut urine has 2-3 times more urea than human waste on Earth. Salt levels are higher. And there’s no sewer system to flush it away. The system has to handle all of this in a sealed, pressurized box floating in zero-g.

Even the way it’s maintained is different. Crew members train for 40 hours before touching a single valve. They learn fluid dynamics, chemical reactions, and how to fix a broken sensor in a spacesuit. Every month, they swap out filters. Every quarter, they check the catalytic reactor. Every year, they do a full system overhaul. Ground teams in Houston watch every reading in real time.

What’s Next: The Next-Gen Water Systems

The current system works-but it’s not perfect. It needs new filters, chemicals, and parts every year. About 120 kilograms of replacement gear. That’s a lot of weight to launch into space. For a Mars mission, you can’t afford to bring that much.

NASA is working on three big upgrades:

• Biological Water Processor: Instead of filters and chemicals, this system uses microbes to eat waste. It’s like a mini sewage plant, but in a jar. Early tests show it could cut consumables by half. Testing on the ISS is planned for 2026.
• Supercritical Water Oxidation (SCWO): This tech uses extreme heat and pressure-374°C and over 200 times Earth’s atmospheric pressure-to turn organic waste into pure water and CO2. Ground tests show it destroys 99.9% of contaminants. The prototype, called SCWO-FPV, will fly to the ISS in 2027.
• Advanced Brine Dewatering System: This one aims for 99.5% recovery by improving the membranes used to pull water from brine. It’s already being tested in labs in Texas and California.

By 2035, NASA expects to have a system that recovers 99.9% of water and needs less than 2% annual replacement parts. That’s the goal for sending people to Mars.

Reliability: The Biggest Fear

Astronauts trust the system. Shane Kimbrough, commander of Expedition 65, said, “The water tastes great and we trust it completely.” An anonymous astronaut in a 2022 survey said, “Knowing our water is safe and abundant lets us focus on science rather than survival.”

But engineers worry. The system has been running since 2008. It’s been reliable-but it’s never had to run for 15 years straight without a single major failure. That’s what a Mars mission needs.

There have been two big breakdowns: one in 2010, when the catalytic reactor failed and recovery dropped 15% for 17 days. Another in 2019, when the brine separator jammed and took three weeks to fix. Most issues are small-clogged filters or sensor drift-and get fixed within two days. But in deep space, a small glitch can become a disaster.

NASA’s 2023 risk report lists water system failure as the third biggest threat to a Mars mission-right after radiation and propulsion.

Why This Matters on Earth Too

You might think this is all about space. But the tech being developed here is already helping Earth.

The membranes used to pull water from brine? They’re being tested in drought-stricken regions. The catalytic reactors that break down chemicals without adding toxins? They’re being adapted for industrial wastewater. NASA estimates these space-born technologies could cut municipal water treatment costs by 15-25%.

It’s not just about surviving on Mars. It’s about learning how to live better on Earth.

Final Thoughts: The Water That Keeps Us Alive

Water recovery systems are the quiet backbone of long-duration spaceflight. No one cheers when the water comes out clean. No one posts selfies with a filter. But without it, no one lives.

The ISS system isn’t magic. It’s engineering-hard, messy, brilliant engineering. It’s a system that turns human waste into something pure. It’s a system that lets astronauts sleep at night knowing they won’t run out of water.

And as we look toward Mars, we’re not just building rockets. We’re building the machines that keep us alive. Because in space, the most important thing isn’t speed. It’s sustainability. And water? It’s the most important thing of all.