When you live 250 miles above the earth on the International Space Station (ISS), how do you get water? It can’t be brought in daily, nor is there room to store large quantities. Yet each astronaut living in the ISS needs about a gallon of water per day for drinking, food preparation, and hygiene. So they have to recycle urine, sweat, and even the water in their breath. “Yesterday’s coffee is tomorrow’s coffee,” is how astronaut Douglas Wheelock described it to the New York Times in 2015.
Not Lost in Space
November 2025 marks 25 years of continuous crews aboard the International Space Station. The largest structure ever built in space, the ISS is the length of a football field and has a mass of nearly a million pounds. But because it’s orbiting the earth at more than 17,000 miles an hour, inhabitants have that falling-roller-coaster sense of microgravity — near weightlessness. Up to six astronauts at a time from the U.S., Russia, Canada, Japan, and Europe live aboard this solar-powered structure, conducting experiments, forecasting weather, and testing technologies.
From pee to tea and back again
The technology for urine recycling on the ISS has developed over the past 50 years. Here’s an overview of how it works: Astronauts pee into a funnel connected to a hose that sucks up urine before it floats away. The collected urine is treated with chemicals to disinfect it and prevent precipitation. Then it’s sent to a urine processor to turn it back into clean water. Urine is 95% water and 5% “other”— urea, uric acid, salts, and waste products — so the processor’s job is to separate the water from the brine. Urine is heated to form steam, which condenses and is collected with the processor’s centrifuge. This cycle takes about 18 hours and recovers 85% of the wastewater it starts with.
Turning pee into drinking water in space may remind you of the science fiction movie Dune. The Fremen of the desert planet wore stillsuits — wearable filtration systems powered by movement — that captured and turned urine, sweat, and breath into drinking water. Though filtration on the space station isn’t as portable as a stillsuit, it gets the job done in real life.
Aboard the ISS, water made in the urine processor is sent to a water processor where it’s further purified and sanitized with iodine. The entire process takes about 8 days, and NASA claims that the resulting water is superior to that of many municipal water systems. At that production rate, however, you certainly wouldn’t want to spill your coffee. If you did, you’d scoop it up and reclaim it before it floats away. In fact, the astronauts even collect and recycle human tears.
Water on Earth is recycled too, but the scale is so much bigger than on a spaceship we might forget that our own drinking water has been recycled countless times. After we drink and urinate, wastewater is (we hope) cleaned, then mixes with groundwater or surface water. From there it evaporates, condenses, and falls as rain. Our planet is its own space ship, relying on a finite amount of water to be shared and cared for by all.
