Water security is a key goal to advance towards sustainable development and an increasingly hard challenge in a climate change context. Achieving water security requires advancing towards equitable access to water services in sufficient quantity and quality to satisfy multiple needs and uses and to ensure the sustainability of such services to various natural and anthropogenic threats. We introduce the notion of ‘territorial water vulnerability’ (TWV) as a measure of the propensity of a particular territory to be or become unable to satisfy relevant water needs and uses adequately as a result of its structural condition to be negatively affected by socio-natural threats and stressors. On this basis, we develop a set of territorial indicators of sensitivity and response capacity for drinking urban water services and apply them to the Gran Valparaiso conurbation on the central coast of Chile. A particularly relevant territory considering the extreme water scarcity of the contributing catchment. A fuzzy logic approach was used to develop a single TWV index at the census block level; through cluster analysis, census blocks profiles are identified whose common characteristics explain their high vulnerability levels. This paper provides at least three relevant contributions to fill gaps identified in the existing literature): (1) an analytical framework to assess urban water security observed from households, considering social dimensions, (2) a methodological approach to carry out high-resolution analysis that considers the ecological, technical and social systems and (3) evidence to guide public policies in the scarcely studied Chilean Case.