Infrastructure-mediated flows (IMFs), such as infiltration and inflow (I&I) of precipitation and groundwater into sanitary sewer systems are difficult to measure and complicate the calculation of urban water budgets. Available I&I quantification methods are based on broad assumptions and do not fully exploit the information content of sensor networks and databases commonly administered by watershed management agencies. This study includes detailed calculations of I&I within 14 tributary basins of the South River Watershed, which has its headwaters in the southeastern portion of the Atlanta Metropolitan Region, USA. The analysis leverages a network of approximately 200 flow meters installed within the sanitary pipes maintained by the DeKalb County Department of Watershed Management. Results revealed little correlation between I&I and watershed attributes, indicating spatial variability which eliminates watershed attributes as indicators of I&I. It is therefore paramount for water managers to use system wide monitoring programs to mitigate the effects of I&I.