Chemical analyses of water samples from 296 wells in the Red River alluvial aquifer indicate that the ground water in the valley is generally hard (more than 120 milligrams per liter) and has a high iron concentration (greater than 6,000 micrograms per liter). The predominant ions found in the water were calcium and bicarbonate. However, in places in the vicinity of Natchitoches, saline water, probably from underlying formations, has infiltrated the aquifer and sodium and chloride are the principal constituents.