In 2003 the Indian environmental researcher Narayana Peesapaty spotted an alarming trend: Groundwater levels in the region of Hyderabad were falling precipitously. He examined rainfall records but found nothing to explain the drop. Looking deeper, he discovered that the culprit was a change in agricultural practices. Many area farmers had abandoned millet—a traditional crop increasingly regarded as “the poor man’s food”—in favor of rice, a thirsty crop that requires 60 times as much water to grow. And because they had access to heavily subsidized electricity, the farmers were continuously pumping water into their fields.