In May 2000, the City of San Antonio passed a $45 million bond issue to purchase land or conservation easements of sensitive land in the recharge zone of the Edwards Aquifer in south central Texas. The Edwards Aquifer is the primary source of water for over 1.7 million people in the region. The application of geographic information systems (GIS) methods allowed for the objective comparison of all properties within the recharge and contributing zones of the aquifer for possible purchase. A GIS matrix was developed and applied in the process of prioritizing sensitive karst lands.