One of the huge challenges for any effort to colonise elsewhere in the solar system is undoubtedly going to be water acquisition; not only for survival but for fuel and construction as well.
Of course survival is the most pressing of these, and as the ISS has proved there's a lot that can be done to recycle water but we still have problems to solve. It's difficult to create a perfect system - water processors and filters wear out over time and need to be replaced, and one breakdown can put everyone's lives in jeopardy even if it's fixable.
This particular look at water recycling highlights one of the unexpected benefits of international collaboration - disagreements leading to redundancy and the opportunity to work through multiple solutions to find the best one.
The space station carries roughly 2,000 liters of water in reserve for emergencies, split about evenly between the U.S. and the Russian sections of the ISS. The two sides operate separate water systems mainly because of decades-old decisions on how best to disinfect water. NASA has decided to switch to silver-ionized water on future missions, but Carter says he likes that there’s both silver- and iodine-treated water aboard the ISS: “It really makes a lot of sense," he says, "to have dissimilar redundancies in the space station in case one of the systems has problems.”