MANY futuristic novels and films have explored what the world might look like without water. But water scarcity isn’t a problem for the far-off future: it’s already here. In its 2021 report, UN-Water outlined the scale of the crisis: 2.3 billion people live in water-stressed countries and 733 million of those people are in “high and critically water-stressed countries”. In 2018 Cape Town, where I live and conduct my research, residents found themselves staring down “day zero”, when household water supplies would run dry. Good rains spared the South African city, but now other parts of the country face similarly…