Two billion people now live in nations plagued by water problems, and almost two-thirds of the world could face water shortages in just four years. The United Nations has long warned that human-driven climate change is leading to severe droughts and more flooding, making water availability increasingly less predictable. In California, the most recent acute dry spell stretched from December 2011 until March of last year. The direst effects took hold in July 2014, with 58% of the state’s land suffering “exceptional drought,” leading to crop and pasture losses and other water emergencies. Water also recently joined gold, oil, and other commodities traded on wall street.