The parched planet: Water on tap

Abstract

In an effort to combat his country's long-standing water crisis, Iran's president took to Twitter last year. "We need plan to save water in agriculture, prevent excessive tap water use, protect underground sources of water and prevent illegal drilling," Hassan Rouhani tweeted in November. Iran is far from alone. From the southwest United States to southern Spain and northern China, water shortages threaten many parts of the world. Nearly 800 million people lack access to safe drinking water and 2.5 billion have no proper sanitation. The situation will probably get worse in coming decades. The world's population is expected to swell from 7 billion today to more than 9 billion by 2050, even as climate change robs precipitation from many parched parts of the planet. If the world warms by just 2 °C above the present level by the end of the century, which scientists believe is exceedingly likely, up to one-fifth of the global population could suffer severe shortages of fresh water. "Even without global environmental change, feeding 9 billion people by 2050 will require an additional 2,000-3,000 cubic kilometres of fresh water in agriculture - more than the total global use of water in irrigation," says Johan Rockström, a specialist on water resources at Stockholm University and director of the Stockholm Resilience Centre. "This equates to nothing less than a new agricultural revolution. Novel approaches, such as water-harvesting practices, are absolutely critical in the future." Most countries are seeking to expand access by tapping the underground aquifers that already supply the bulk of the fresh water for the global population. At the same time, some are experimenting with recycling waste water for agriculture and other uses. But many nations hope to tap unconventional sources - ranging from fog to the ocean - to quench their thirst. Some approaches involve billion-dollar deals; others are local efforts that require little in the way of costly technology. Here Nature looks at five ways to produce fresh water from unusual sources. © 2014 Macmillan Publishers Limited. All rights reserved.