If Iran is in the news because of its nuclear program, the greatest threat to the country’s well-being isn’t economic sanctions or the Sunni-Shiite schism. Rather, the greatest threat to Iran may be that the country is running out of water. The problem is so severe that social unrest, economic dislocation, even out migration can all be imagined. One government advisor recently predicted that as many as fifty million Iranians—seventy percent of Iran’s population—may be forced to leave because of a lack of water. Water problems are a proxy for bad governance, and Iran has water problems galore. By contrast,...