In June 2013, Jay Parikh, the head of Facebook’s infrastructure and operations team, received a call about the company’s new data center in Prineville, Oregon. “Jay, there’s a cloud in the data center,” the caller said. “What do you mean—outside?” Parikh asked. “No,” the caller said. “Inside. It was raining in the data center.” In Prineville’s first summer of operation, the combination of high temperatures, low humidity, and a water-based cooling system led to the condensation of evaporated water in the aisles among the servers, creating indoor clouds.