THOUSANDS have lived without love, not one without water,” so W. H. Auden finished his poem “First Things First.” And right he was. Only oxygen is needed more urgently than water at most times. But a key difference that makes water a more immediate subject for theorists of justice is that, for now, oxygen is normally amply available where humans live. Historically, the same was true of water since humans would not settle in places without clean water. Nowadays, however, water treatment plants and delivery infrastructure have vastly extended the regions where humans can live permanently. Population increases have prompted people to settle in locations where access to clean water is precarious.