This article discusses how the notion of "diffusionism" has functioned as a straw man in the history of technology. This has prevented it from becoming fully global and symmetrical. In contrast, the second section of this article offers an example of what a symmetrical account of the global history of technology might look like, using the case of chlorination in the early twentieth century. Focusing on London, Bogotá, and Jersey City, it shows that chlorination was initially rejected in each of these places but was later adopted in all of them for economic reasons after discussions that took the same form. It concludes by suggesting that global histories of technology must treat North and South, East and West, center and periphery, and metropole and colony symmetrically, drawing out similarities and differences based on the available evidence without assuming them in advance.