Nature is the unseen dimension of the nexus. With its functions integral to the three securities and their inter-dependence, nature is part of the infrastructure needed to manage the nexus and its resilience. Nature helps mediate the nexus links, by storing, moving, cleaning and buffering flows of water, making drought and flood less severe, and food and energy production more reliable. Without healthy ecosystems in well-functioning watersheds, the infrastructure built for irrigation, hydropower or municipal water supply does not function sustainably, and is unlikely to achieve the economic returns necessary to justify investments.