Water on the Space Station
Mimicking Mother Earth
When water evaporates from the ocean and surface waters, it leaves
behind impurities. In the absence of air pollution, nearly
pure water falls back to the ground as precipitation.
On Earth, water that passes through animals' bodies is made fresh again
by natural processes. Microbes in the soil break down urea and
convert it to a form that plants can absorb and use to build new
plant tissue. The granular soil also acts as a physical filter.
Bits of clay cling to nutrients in urine electrostatically, purifying
the water and providing nutrients for plants.
Water excreted by animals also evaporates into the atmosphere and rains back
down to the Earth as fresh water -- a natural form of distillation.
Water purification machines on the ISS partly mimic these processes, but they do
not rely on microbes or any other living things.
"While you try to mimic what's happening on Earth -- which is so complicated
if you really think about it -- we have to use systems that we
can control 100 percent," said Monsi Roman, chief microbiologist
for the ECLSS project at MSFC. ECLSS depends on machines -- not
microbes -- because, "if a machine breaks, you can fix it.
The water purification machines on the ISS will cleanse wastewater in a
The first step is a filter that removes particles and debris. Then the water
passes through the "multi-filtration beds," which contain substances
that remove organic and inorganic impurities. And finally, the
"catalytic oxidation reactor" removes volatile organic compounds
and kills bacteria and viruses.