Ground water is one of the most valuable and abundant natural resources of Louisiana. Of the 4-.4 million people who live in the State, 61 percent use ground water as a source for drinking water. Most industrial and rural users and half of the irrigation users in the State rely on ground water. Quantity, however, is not the only aspect that makes ground water so valuable; quality also is important for its use. In most areas, little or no water treatment is required for drinking water and industrial purposes. Knowledge of Louisiana's ground-water resources is needed to ensure proper development and protection of this valuable resource. This report is designed to inform citizens about the availability and quality of ground water in Louisiana. It is not intended as a technical reference; rather, it is a guide to ground water and the significant role this resource plays in the state. Most of the ground water that is used in the State is withdrawn from 13 aquifers and aquifer systems: the Cockfield, Sparta, and Carrizo-Wilcox aquifersin northern Louisiana; Chicot aquifer system, Evangeline aquifer, Jasper aquifer system, and Catahoula aquifer in central and southwestern Louisiana; the Chicot equivalent, Evangeline equivalent, and Jasper equivalent aquifer systems in southeastern Louisiana; and the MississippiRiver alluvial, Red River alluvial, and upland terrace aquifers that are statewide. Ground water is affected by man's activities on the land surface, and the major ground-water concerns in Louisiana are: (1) contamination from surface disposal of hazardous waste, agricultural chemicals, and petroleum products; (2) contamination from surface wastes and saltwater through abandoned wells; (3) saltwater encroachment; and (4) local overdevelopment. Information about ground water in Louisiana is extensive and available to the public. Several State and Federal agencies provide published and unpublished material upon request.