Water, and its absence, has become Iran’s national obsession. In the mosques of northern Tehran the imams have been praying for rain, while the meteorologists count down the hours until the weather is forecast to break and rain is finally due to fall from the sky. Forecasts of “rain-producing clouds” are front-page news. More than 50 days have passed since the start of Iran’s rainy season and more than 20 provinces have not yet had a drop. The number of dams that have less than 5% of their reservoir capacity had increased from eight to 32, and the crisis has...