This article maps a meshwork of formal and informal elements of places called Disadvantaged Unincorporated Communities (DUCs) to understand the role of informality in producing unjust access to safe drinking water in California’s San Joaquin Valley. It examines the spatial, racial, and class-based dimensions of informality. The paper aims to both enrich the literature on informality studies and use the concept of informality to expand research on DUCs and water access. We use socio-spatial analyses of the relationships between informality and water justice to reach the following conclusions: DUCs face severe problems in access to safe drinking water; disparities in access have a spatial dimension; inequities in water access are racialised; the proximity of DUCs to safe drinking water offers good potential for improved water access; and the challenges of informality are targeted through water justice advocacy and public policy.