Water Recovery System (WRS)

On the International Space Station, today’s coffee might have been yesterday’s sweat. The Water Recovery System is the machinery that makes that possible — turning wastewater back into clean drinking water so a crew in orbit needs far less shipped up from Earth.

Quick facts

• What it does: Reclaims wastewater (crew urine, cabin humidity, and other waste streams) and purifies it into safe drinking water.
• Recovery rate: About 93–94% of the station’s water before the brine processor was added; NASA demonstrated 98% recovery in 2023 — the level it considers necessary for crewed Mars missions.
• Built by: Primarily NASA, as part of the station’s regenerative ECLSS (Environmental Control and Life Support System — the equipment that keeps air and water safe for the crew).
• Core assemblies: the Urine Processor Assembly (UPA), the Water Processor Assembly (WPA), and later the Brine Processor Assembly (BPA).
• Launched: aboard Space Shuttle Endeavour on STS-126, November 14, 2008; operational November 25, 2008.
• Daily need: roughly one gallon (~3.8 liters) of water per crew member per day for drinking, food prep, and hygiene.

What it is and how it works

Wastewater is gathered from several sources: crew urine, cabin humidity condensate (moisture from breath and sweat captured by dehumidifiers), and other waste streams.

Urine goes first to the Urine Processor Assembly. It uses low-pressure vacuum distillation — boiling the water out of urine at reduced pressure — paired with a spinning centrifuge that separates the liquid from the vapor. (On Earth, gravity does that separating for you; in orbit, the spin stands in for gravity.) The UPA is designed to handle about 9 kilograms of urine per day, enough for a six-person crew.

The recovered vapor, now distilled water, joins the collected humidity condensate and flows to the Water Processor Assembly. There the water passes through multifiltration beds (filters and ion-exchange media that strip out particles, salts, and organic compounds), then through a high-temperature catalytic reactor that breaks down trace organics like alcohols. Sensors check the result: if it meets standards, the water is dosed with iodine to suppress microbial growth and stored as drinking water; if not, it is sent back through.

The concentrated leftover from the UPA, called brine, goes to the Brine Processor Assembly. Warm, dry air evaporates still more water out of that brine, and a filter separates the contaminants from the water vapor. Capturing that last, hardest fraction is what pushed total recovery to 98%.

Why it matters

Water is heavy and expensive to launch, so recycling it onboard sharply reduces resupply cargo and cost. This idea of reusing resources instead of constantly shipping new ones is called “closed-loop” life support, and water recovery is its cornerstone. On the station, the WRS keeps a continuous crew supplied while needing far less water flown up.

It is also a proving ground for deep-space travel. NASA estimates that a crewed Mars mission must reclaim at least 98% of its water, because resupply along the way is impossible. The 2023 Brine Processor demonstration hit exactly that figure, directly validating the technology behind the Artemis lunar program and future Moon and Mars habitats — anywhere every drop must be reused.

Notable examples and challenges

• International Space Station: the WRS is a core part of the regenerative ECLSS, first installed in the Destiny lab and relocated to the Tranquility (Node 3) module in February 2010.
• STS-126 (November 2008): Space Shuttle Endeavour delivered and installed the hardware.
• Brine Processor Assembly: a NASA technology demonstration, delivered on Northrop Grumman’s Cygnus NG-15 resupply mission, that reached the 98% milestone.
• Volatile Removal Assembly: flown on STS-89 (January 1998) to test the catalytic reactor in microgravity.

The system has not been trouble-free. The UPA’s distillation assembly failed one day after its 2008 installation and was repaired by March 2009. Early on, elevated calcium in crew urine caused calcium-sulfate scaling that fouled the UPA, forcing operation near 70% — below the original 85% target — until process and pretreatment changes fixed it. Pretreatment chemicals added to control microbes and scaling then have to be removed downstream, and small losses are still topped up by water from Earth and by water made as a byproduct of the Oxygen Generation System. The loop is nearly closed — and squeezing out the final few percent is exactly the hard regime a Mars crew will live in.