This chapter analyzes the importance of urban smellscapes for early modern technological innovation, proceeding from the idea that cities did not only consist of people, impressive buildings, and industry, but also of excrements, public toilets, and air pollution. It attempts to draw different historiographical traditions together, and to reveal the existing kinship between the early modern period and later developments. The chapter explores the argument is that certain smells were typical for a city; that these smells led to specific reactions by city dwellers and local authorities; and that, along these lines, urban odors played a decisive role in the development of new technologies. It provides a comparison between two major Dutch cities: Leiden, an industrial center for textile processing, and Batavia, the Republic’s colonial headquarters in the East Indies. The chapter deals with the Leiden experience of malodorous water by analyzing a series of plans for the amelioration of water flow in the canals.