Within policy circles, people often bandy about the term “water-energy nexus.” Like most wonk-speak, it’s a rather complex way to express a simple relationship. Energy production requires a tremendous amount of water, almost on par with irrigated agriculture. And water production needs a lot of energy, for pumping, treating, and transportation. They’re interdependent. And therein lies the problem. We asked the U.S. Department of Energy’s Michael Knotek, the deputy under secretary for science and energy and a scientist himself, how to plan for a future in which we’ll demand a lot of both.