By the end of the eighteenth century the majority of households in London received a piped water supply. This article examines the geographical, technological, and environmental challenges that London’s private water companies faced as they created and expanded the large technological networks necessary to provide the growing city’s water supply. It identifies geography and drought as the main drivers of innovation in London’s water supply neworks, and argues that the main impediment to expansion for the majority of the water companies was overcoming the differences in elevation between their intake points and customer bases, with major improvements often made as a result of water shortages. The timing and the success or failure of a company’s technological improvements proved pivotal in the subsequent development of the water market.