The City of San Antonio relies heavily on groundwater supplies from the Edwards Aquifer to meet water demands. The Edwards Aquifer recharges quickly, has a close hydraulic connection between recharge and springflow, and is susceptible to droughts. San Antonio is expecting a 51% increase in population over the next 25 years with a 40% increase in projected water demands. For this reason, San Antonio must continually evaluate water management strategies of the Edwards Aquifer and impacts of drought on water supplies to ensure adequate water supply during future drought conditions. Use of water from the Edwards Aquifer is constrained by water levels in key index wells and minimum springflow requirements for Comal Springs, the largest spring in Texas. In an effort to maintain springflow above critical levels, the Edwards Aquifer Authority has implemented rules that require pumping reductions for municipal, industrial, and irrigation users on the basis of water levels at key index wells and springflows. GWSIM4 has been used by SAWS to evaluate water management scenarios, including impacts of changes to Edwards Aquifer Authority rules, transfers of irrigation rights for municipal use, aquifer storage and recovery, and use of quarries for recharge to the Edwards aquifer to enhance water levels and springflow.  For example, GWSIM4 was used by SAWS to evaluate changes in average annual groundwater supplies and Comal springflow in response to increasing Edwards pumping scenarios. These model analyses included modifying annual pumping for various water users in each county and evaluating various water level and springflow triggers with associated pumping reductions ranging from 5 to 30%, based on drought severity. This presentation will consider various applications of using a groundwater model as a management tool to predict impacts of alternative water supply project scenarios on water levels and springflows to protect public welfare and ecological sensitivities.