Edwards aquifer

An arch-shaped belt of porous, water bearing limestone composed of the Comanche Peak, Edwards, and Georgetown formations trending from west to east to northeast through Kinney, Uvalde, Medina, Bexar, Comal, Hays, Travis, and Williamson counties.


Source: Corrosion-Doctors.org

Wikipedia:  https://en.wikipedia.org/wiki/Edwards_Aquifer