In space, water is one of the most valuable resources.
The International Space Station (ISS), orbiting roughly 240 miles (or 400 km) above Earth, hosts astronauts for months at a time.
So how do astronauts get water in space, and how do they make sure they never run out?
In the early days of space exploration, astronauts carried their water in metal canisters and soft plastic bags. During NASA’s Apollo missions to the Moon, water was stored in stowage tanks and used sparingly, not just for drinking but also for rehydrating meals and cooling space suits.
These early systems were heavy and limited. Skylab, America’s first space station in the 1970s, had to ration water carefully due to its limited resupply capabilities. Back then, water wasn’t recycled. Once used, it was gone.
The Cost of Sending Water to Orbit
During the Space Shuttle era, launching cargo into orbit cost around $10,000 per pound. Since a gallon of water weighs about 3.8 kilograms, or 8.4 pounds, that put the price of sending a single gallon into space at over $83,000 USD. This estimate comes from the early 2000s.
While launch costs have fallen dramatically with newer rockets like SpaceX’s Falcon 9, bringing the cost of launching a gallon of water down to roughly $10,200 USD, it’s still a heavy and costly resource to send off-planet.
Each astronaut needs about 0.93 gallons (3.5 liters) of water per day for drinking, preparing food, and hygiene. Multiply that by six crew members and a six-month mission, and you’re looking at nearly 1,000 gallons (or more than 3,700 liters).
This demand led to the development of one of the most advanced and efficient water recycling systems ever built: the Environmental Control and Life Support System (ECLSS) aboard the ISS.
The Science of Water Recovery
This system captures water from multiple sources, including urine, sweat, exhaled breath, and even moisture from towels or cabin humidity.
The process begins with the Urine Processor Assembly (UPA), which spins liquid in a rotating distillation unit to simulate gravity. This separates out the water vapor. The vapor is then condensed and passed to the Water Processor Assembly (WPA), where a series of filters and chemical treatments remove any trace contaminants.
The result is crystal-clear water that meets or exceeds U.S. drinking water standards. In 2023, NASA confirmed that the ISS had reached a 98% water recovery rate meaning virtually all water on board is recycled.
Astronauts often describe the recycled water as indistinguishable from bottled water. That’s not just a technical achievement, it’s a life-supporting breakthrough.
Planning how much water to send and how much to recover is critical for mission design. Engineers must consider daily use, crew size, mission duration, and emergency reserves to ensure sustainability in orbit.
Shaping the Future of Space
What makes this innovation even more important is how it’s shaping the future. NASA’s Artemis missions to the Moon, and the eventual goal of reaching Mars, hinge on systems like those tested on the ISS. Water can’t be resupplied easily on a lunar base or a Martian habitat.
Future life-support systems will rely even more heavily on closed-loop recycling. Engineers are already experimenting with ways to integrate these systems into surface habitats, combining recycled water with in-situ resources like ice mined from lunar soil.
These systems aren’t just about cost savings. They are about independence and allowing astronauts to live and work far beyond Earth, without relying on constant support.