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Have you ever wondered about plumbing in space? Which way does water flow in a weightless environment? Can toilets flush in free-fall? Here on Earth, plumbing is something most of us take for granted. Turn the faucet and water comes rushing out. Flush the toilet and water disappears. On the International Space Station, it's not that simple. And if you spring a leak, the plumbers are all at least 235 miles (378 km) and a rocket launch away.
Designers of the Station had to contend with these problems as they laid out a complex network of tubes, pipes and ducts between the Station's outer skin and its inner walls. Like veins and arteries in the human body, the Station's plumbing circulates vital liquids and gases that keep the crew and the Station in good health.
Most of the time the Station has to operate completely on its own. Shuttle visits bring new supplies and equipment, but between visits the Station runs on a fixed amount of air and water. That means the Station must operate efficiently. The Shuttle's cargo capacity is limited and valuable, so recycling on the Station is necessary to reduce the supplies of water and air it needs. While a house on Earth can drain its wastewater to sewer lines that take the wastes to a municipal treatment plant, the Station must have its own water treatment plant.
Efficient, leak-free recycling of everything that flows through the Station's pipes is essential. This network of tubing and hardware, which is far more elaborate than that of the typical house, must be compact, lightweight, corrosion-resistant, leak-resistant, microbe-resistant, and highly dependable. To meet this tall order, the pipes of the Space Station are made from titanium, stainless steel, or Teflon wrapped in metal mesh. In comparison, household plumbing is typically made of inexpensive PVC and copper.
The plumbing on the Station must also operate without the assistance of gravity. When building a house on Earth, it's enough to just lay the pipe and then let gravity or the pressure of the city water supply create the flow. In the free fall of Earth orbit, liquids and gases would stay in the pipes and stagnate.
Dave Williams is system manager for Environmental Control and Life Support Systems (ECLSS) at Johnson Space Center in Houston, Texas. He says, "You have to look at the lack of gravity carefully, because normally fluids would just sit there, unless you had the head pressure to force them. In a house, you can count on gravity when you flush a toilet to take that water and put it out in the sewer."
To keep the fluids flowing, the Station's plumbing system includes dozens of pumps and fans that create the pressure needed to keep the liquids and gases moving.
The plumbing must also have a higher level of cleanliness than systems on Earth. The Station system recycles the urine of the crew and laboratory animals and returns the water, purified, to the drinking supply. The health of the crew is of particular concern in space. Like plumbers, there are few doctors nearby! Microbes are a danger even to the Station itself, as shown by the problems on Mir with fungal growth. Keeping microbe levels in the water supply to an absolute minimum is a necessity. The Station's water recycling system results in sterile, contaminant-free water that is much cleaner and safer than the average tap water on Earth.