The Ohio River alluvium is the best source of groundwater in the county. Many properly constructed drilled wells will produce several hundred gallons per minute from the alluvium, with most wells able to produce enough for a domestic supply at depths of less than 100 feet. Water is hard or very hard, but otherwise of good quality. In the main sections of the larger creek valleys, in some of the Ohio River bottoms, and on broad ridges in a limited area south of the towns of Skylight and Crestwood, most drilled wells will produce enough water for a domestic supply at depths of less than 100 feet. Some wells located in the smaller creek valleys and in some broad ridges in western and central Oldham County will produce enough water for a domestic supply, except during dry weather. In upland areas of the rest of Oldham County, about half the county, most drilled wells will not produce enough water for a dependable domestic supply, unless they are drilled along drainage lines, in which case they may produce enough water except during dry weather. Groundwater in these areas is hard or very hard, and may contain salt or hydrogen sulfide, especially at depths greater than 100 feet.