Water is essential for life. A typical adult drinks a liter per day to maintain their health—two or more liters in hot desert conditions. Americans consume almost 400 liters per person per day for drinking, cooking, washing clothes and bathing.
Water use aboard the International Space Station is more constrained. Astronauts get by with about four liters per day for drinking, cooking, tooth brushing, and general hygiene. Personal water use in a Mars base will be similarly restricted, with the caveat that any long-term occupancy will require this life-giving fluid to grow crops—lots of it.
Early missions—two month’s duration on-planet—will bring their own water. Alternately, water, food and medical supplies will be prepositioned, shipped with the habitat modules. But as missions extend and bases are permanently occupied, an alternate supply will be needed.
We think of the Red Planet as an arid world, but that only holds true for the liquid phase. The North Polar ice cap contains as much as 300,000 cubic miles of water ice. Hellas Planitia, the setting for the EPSILON series, may at one time have contained an ocean. Today, vast glaciers are believed buried under up to a kilometer of dust and regolith. Even in equatorial regions, water ice lurks underground or in always shaded areas. It makes more sense to mine ice and melt it than it does to transport what's needed for along-term presence from Earth.
But all that Martian water comes with impurities. Soils, dust, and ice are all contaminated with perchlorates. These toxic powerful oxidizers are chemically comparable to chlorine bleach. In addition to perchlorates, all that dust blowing around contains plenty of heavy metals. The Red Planet’s water, before it can be used, must be purified. And once it’s been consumed, it will have to be purified again to filter out urine salts.
The ISS utilizes a two-tier reclamation system unimaginatively called the Water Recovery System. The first subsystem collects vapor from breath and sweat in a dehumidifier. From there it’s condensed and directed to the Water Processing Unit which produces potable water.
A second component, the Urine Processor Assembly, uses vacuum distillation to extract water vapor. The concentrated brine is then osmotically filtered. The purified liquid that collects on the membrane surface is heated, vaporized and added to the WPU, leaving the salts behind. After adding iodine, the reclaimed water is returned to use by the crew.
It should be noted that even though the ISS recycles 98% of its water, all solid waste (poop) is either burned or flown to Earth for study. No closed loop there—yet.
So, what treatment method is most likely to be employed on Mars? Hauling mass to the Fourth Rock from the Sun will be an expensive proposition. That includes water. As a result, the amount will be highly constrained. Recycling systems on the ISS and refined on the Moon during the Artemis Program will recycle this precious commodity.
A pretreatment step to remove perchlorates and heavy metals will be needed if the base uses Martian ice for its water supply. I expect NASA will test to determine if perchlorates can be removed using the Urine Processor Assembly.
Unlike on the ISS, concentrated pee will become a resource on Mars. After garden modules are established to support long-term missions, it will serve as fertilizer. Care will have to be taken to exclude from waste water the heavy metals and perchlorates introduced into the habitats through EVAs. Those contaminants would render urine salts unusable.
I use humans to monitor these systems in the EPSILON SciFi Thriller Series. In reality, they’ll be monitored and regulated with AI as the size and duration of human presence on the Red Planet expands.
The next time you pour yourself a glass of tap water, consider what it would take to reuse it if that was all you got for months on end.
Next month’s topic: Thermal Management on Mars. ‘til then,
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Want a deeper dive? Check out these sources.
https://www.nasa.gov/missions/station/iss-research/nasa-achieves-water-recovery-milestone-on-international-space-station/#:~:text=Each%20crew%20member%20needs%20about,hygiene%20such%20as%20brushing%20teeth.
https://en.wikipedia.org/wiki/Urine
