In Frank Herbert's science fiction classic, Dune, the inhabitants of the titular desert planet survive by wearing "stillsuits" that recycle every drop of water they excrete, coupling ecological temperament with martial discipline. Water is vital to life as we know it. That's why our search for aliens focuses on worlds that harbour it (see page 29), or once did (page 8), as does our search for worlds on which we might one day settle. Hence the difficulty in finding economic models for responsible water use: how do you agree a fair price for such a vital commodity?
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