This dissertation explores the regional ecological politics of water scarcity during the 2011-2017 California drought. Based on over two years of ethnographic fieldwork, I center my coordinated case study on Southern California’s underserved peripheral zones: small, groundwater-dependent communities in the rural desert, which have (at most) 50 years of viable water left. My ethnography follows community activists, policy makers, water scientists, technicians, and resource managers as they work to understand, protect, and sustain their local water. By examining water socialities in a region notorious for drought, I show that our existing explanatory models of water scarcity are insufficient to understand the lived reality of contemporary water politics in the Western United States. Instead, I apprehend California water through I call “ecology building”: a process incorporating scientific knowledge production, historical practices, political projects, and the changing material qualities of the environment itself. Scientific and policy experts have used the term “hidden drought” to call attention to California’s rapidly decreasing groundwater. I argue that hidden drought is not just about unseen water depletion. Instead, hiddenness emerges through more complex forms of invisibility or absence: remotely sensed water data, unseen hydrological infrastructure, deep histories, archival laws, secretive political regimes, and exclusionary policies. In so doing, I show how the problem of a perpetual lack of water shapes social and political life in a diverse cross section of communities. Here, an ad-hoc regional network of activists and water experts must navigate a constantly shifting, highly technical process involving diverse stakeholders, deep political allegiances, tangled regulatory agencies, millions of dollars of scientific research, and decades of litigation. My data draw from a broad cross-section of groundwater cases, linked by a shared environment and a shared network of water experts. My longterm engagement with the region, and the breadth of my work with water scientists, technicians, policy makers, and activists, allow me to provide analysis that cuts across normally disparate registers of water expertise, drawing together the complex community politics of water governance with the highly scaled technological politics of water monitoring and modeling.