This thesis compares the Roman water systems in Pompeii and Nîmes in order to understand the relationship of the water systems to the urban layout of the city. Analyzing the nature and location of an urban water system enables a better understanding of the urban functions within a city, as well as prediction of the nature and location of particular structures within an urban plan. I examine the primary sources of Vitruvius and Frontinus, the topography of each city, the urban orientations, the hydro-technologies employed, and the public and private buildings to which water would have been supplied. My survey of water systems begins with the source of water and the aqueduct that supplies each city and also assesses the relationship of the aqueduct to the rural landscape. In both Pompeii and Nîmes, water from the aqueduct is deposited in a central settling tank within the city and dispersed from the settling tank to various destinations. I have analyzed the buildings, public and private, that had or would have required direct access to this water source and created water supply routes for each colony.