How the ISS Recycles Water (Including Urine)

Sending water to space is expensive. It costs roughly $20,000 to launch a single kilogram to the ISS, and water is heavy. That is why the station has a sophisticated water recovery system that recycles about 90% of all water on board - turning wastewater, humidity, and even urine back into clean drinking water.

The Water Recovery System

The Environmental Control and Life Support System (ECLSS), located primarily in Node 3 (also called Tranquility), handles water recycling. It has two main subsystems:

• Water Processor Assembly (WPA) - Takes in wastewater (including processed urine, humidity condensate, and hygiene water) and produces clean drinking water through filtration, catalytic oxidation, and iodine treatment.
• Urine Processor Assembly (UPA) - Uses vacuum distillation to extract water from urine. The process heats urine in a low-pressure environment, causing the water to evaporate while contaminants stay behind. The resulting distillate is then sent to the WPA for final processing.

The numbers

The ISS crew of six to seven people needs about 12 liters of water per person per day for drinking, food preparation, and hygiene. Without recycling, that would mean launching more than 30,000 kilograms of water per year.

With the current recycling system, the station recovers about 3.6 liters of water from urine per crew member per day, plus additional water from humidity and other sources. The overall recovery rate is around 90%, which saves millions of dollars in launch costs annually.

What the tank levels mean

On ISS Monitor, you can see three water-related metrics:

• Urine Tank Level - Shows how full the urine collection tank in Node 3 is. When it reaches a certain threshold, the Urine Processor Assembly kicks in to process the contents.
• Waste Water Level - The amount of wastewater waiting to be processed by the Water Processor Assembly.
• Clean Water Level - Processed, drinkable water ready for use by the crew.

You will notice these levels fluctuate throughout the day as the crew uses water and the recycling systems process it. If you watch over several days, you can see the cyclical pattern of collection and processing.

Is the water safe?

NASA says the recycled water on the ISS is actually cleaner than most tap water on Earth. It goes through multiple stages of filtration and treatment, and is regularly tested by the crew using on-board analysis kits. Astronauts have said it tastes fine - and most try not to think too much about where it came from.

As NASA prepares for longer missions to the Moon and Mars, the water recycling technology developed on the ISS will be essential. A Mars mission would need to recycle water for two to three years without resupply, pushing recovery rates even higher than what the station achieves today.