Los Angeles County (LAC) is the largest urban population center in the water-stressed Western United States. Here, LAC is used as a testbed to explore how population growth, urban expansion and densification, and future water supply interact to influence water shortage outcomes. The first component of this work involves generating future decadal water demands from 2030 to 2100 using population and urban morphology evolution raster datasets for LAC associated with the shared socioeconomic pathways (SSP) scenarios. We use population projections within water provider regions to drive indoor water demand growth, while outdoor demand is projected using green fraction water demand-urban land class relationships established using high-resolution landcover data for LAC that are applied to the urban morphology projections. The second component of this study uses a network flow optimization model, building off the existing Artes model of LAC’s water supply system, to interrogate how LAC’s water system responds to changes in future demand and supply. The model represents over 70 water utilities that supply water to over 10 million people. The water supply network is resolved using a network of 342 nodes representing sources of supply or demand, and 717 links that define node topology and link-specific conveyance capacities, and runs at monthly resolution. Presently, most of LAC’s water is supplied from a combination of local groundwater and imported surface water. However, LAC’s dependence on imported water from Northern California and the Colorado River exposes it to potential shortages during severe or prolonged drought conditions that reduce availability of imports. Due to deep uncertainty around future imports, we take an exploratory modeling approach where historical imports over a 25-year period (1986-2010) are scaled (increased or decreased) and applied to the future demand scenarios reflecting population growth and changes to urban morphology. The resolution of the model allows us to not only quantify the frequency and magnitude of shortages for LAC as a whole, but also to characterize provider-level vulnerability due to differences in provider supply sources (ex. Imports, reservoirs, groundwater, reuse), and under scenarios of potential expansion of water reuse and a variety of future urban morphologies. An eventual application of this work is to couple irrigation supply to the Weather Research and Forecast Urban Canopy Model (WRF-UCM) to investigate implications of long-term urban morphology changes and water supply reductions during drought for urban heat. This research is performed under the IM3 project, funded by the MSD program area in EESM.