Iran is in the midst of its worst drought in 30 years, heightening problems caused by poor water management, climate change, and rapid population growth. The country’s largest body of freshwater, Lake Hamoun, is now desert and 100 nearby villages are disappearing beneath sand. Drinking water is being rationed in more than 30 cities, including Tehran. Last year, with its crops failing, Iran became the world’s largest importer of wheat. Inefficient water use in the country is part of the problem. About 70 percent of water used for irrigation is wasted. And in recent times, per capita water use in Tehran has been 63 gallons a day, compared to about 32 gallons in Western Europe, according to the U.N.