|Abstract:||This report gives a summarized description of the public water supplies in 42 counties of southern Texas, extending from the Rio Grande northward to the northern boundaries of Kinney, Uvalde, Bandera, Kendall, and Hays Counties and eastward to the eastern boundaries of Caldwell, Gonzales, De Witt, Victoria, and Calhoun Counties. It gives the available data as follows for each of the 114 communities: Population of the community; name of the official from whom the information was obtained; ownership of water works, whether private or municipal; source of supply, whether ground or surface water; the amount of water consumed; the facilities for storage; the number of customers served; the character of the chemical and sanitary treatment, if any; and chemical analyses of the water. Where ground water is used, the following information also is given: Records of wells, including drillers‘ logs; character of the pumping equipment; yield of the wells and records of water levels, where they are available.
The communities served by these public supplies had a population of 668,000 in 1940. Ground water is used by 79 of these communities and surface water by 31. The total amount of water consumed averages about 95 million gallons a day, of which about 55 million gallons is obtained from ground water and about 40 million gallons from surface water.
The extreme northern part of the region lies on the Edwards Plateau, and the remainder lies within the Gulf Coastal Plain. The rocks that crop out in the region are practically all sedimentary and consist chiefly of limestone, shale, clay, sandstone, sand, and gravel. They range in geologic age from Lower Cretaceous to Quaternary.
The general geologic structure of the region is comparatively simple. The most prominent features are the regional gulfward dip of the formations at an angle greater than the slope of the land surface, which is a significant factor governing the occurrence of artesian water, and faulting along the Balcones fault zone which controls the occurrence and movement of ground water in the Edwards and associated limestones.
Among the most important aquifers are the Edwards limestone of Lower Cretaceous age; the Carrizo sand, sands of the Mount Selman formation, the Oakville sandstone, and the Goliad sand of Tertiary age; and the Lissie formation and sands of the Beaumont clay of Quaternary age. Each of these units has outcrop areas from which the beds dip beneath younger formations to increasingly greater depths.
For convenience in summarizing the sources of municipal water supplies, the region has been divided into four areas, as shown on plate 1. In area A, Bandera obtains its water from sands in the Trinity group; Divine in southeastern Medina County obtains water from sands in the Wilcox group or the Carrizo sand; and Boerne in southern Kendall County obtains its supply from Recent alluvium. The remainder of the municipalities in the area obtain water from the Edwards limestone, which has the greatest perennial yield of any aquifer in Texas. In area B, the Carrizo sand is the important aquifer in most of the area, although in the northeastern part several towns that are above the outcrop of the Carrizo sand obtain water from sands in the Wilcox group. In area C, all of the cities and towns use surface water with the exception of Falls City, Gonzales, and Three Rivers. In area D, which is adjacent to the Gulf Coast, the principal sources of ground water are the Catahoula tuff, the Oakville sandstone, sands of the Lagarto clay, the Goliad sand, the Lissie formation, and sands of the Beaumont clay. Most of the public supplies obtained from surface water in Southern Texas are filtered and frequently are given further treatment that alters the chemical character of the water. All except two of the supplies from the Rio Grande are given some chemical treatment and about two-thirds of them are filtered. Of the 182 analyses given in this report, 138 are from we