This article examines specific ways in which sanitation infrastructure matters politically, both as a set of materials and as a discursive object in colonial and post‐colonial Bombay. It reflects on a history of sanitation as a set of concepts which can both historicize seemingly ‘new’ practices and shed light on the contemporary city. It considers two moments in Bombay’s ‘sanitary history’— the mid‐nineteenth century and the present day — and elucidates the distinct and changing spatial imaginaries and logics of sanitation in their broad relation to urbanization and nature. It conceptualizes colonial discourses of a ‘contaminated city’ and public health, and finds productive sites of intersection between these discourses and contemporary debates and practices in Bombay, including bourgeois environmentalism, discourses of the ‘world city’, and logics of community‐managed sanitation infrastructures. It also highlights an important role for urban comparativism, in the context of different imaginaries and logics, in both cases. By connecting infrastructure, public health discourses and modes of urban government, the article traces a specific historical geography of cyborg urbanization that is always already splintered, unequal and contested. For the urban poor in particular, much is at stake in how the sanitary city is constructed as a problem, how the solutions to it are mobilized, and how improvement is measured.