Edwards Aquifer

The total surface area overlying the Edwards Aquifer is approximately 3,600 square miles. The District oversees the Barton Springs segment of the aquifer and the Edwards Aquifer Authority manages the southern portion. 

Overview of the Aquifers

The Edwards and Trinity aquifers are karst aquifers, which form from the gradual dissolution of soluble rock, such as limestone, resulting in unique features like caves and sinkholes. Precipitation runoff enters these landscapes to become groundwater. Surface pollutants can easily run off, enter local aquifers, and contaminate precious groundwater resources. It’s important for each of us be mindful of our actions above ground to protect this natural resource for community members and local ecosystems alike.


While these aquifers can commingle due to faulting, they are primarily separated by layers of rock, also known as “confining layers”. The Edwards Aquifer lies above the Trinity Aquifer in the majority of our District. In the Western portion of our region in Hays County, part of the Edwards have eroded away, leaving the Trinity near the surface.