Ground water that emanates from carbonate bedrock in the Scioto River drainage basin is characterized by 87Sr/86Sr ratios in the range of 0.708 to 0.709; usually high Sr/Ca ratios in this water identify celestite lenses within the carbonate bedrock as the dominant source of strontium. Ground water from clastic bedrock, principally shale, has 87Sr/86Sr ratios that vary from about 0.710 to about 0.713 and shows low Sr/Ca ratios. Thus, there are two basic ground-water types that emanate from bedrock within the basin. They can be identified by these two parameters. Most ground water that has been in contact only with glacial till, which covers the northern two-thirds of the basin, has carbonate-type 87Sr/86Sr ratios as well as high Sr/Ca ratios. Celestite is apparently present in the till throughout much of the Scioto basin. Ground water that contains celestite-derived strontium, whether from the carbonate bedrock or the till, has so great a strontium content as to control completely the 87Sr/86Sr ratios of surface water northwest of the glacial boundary. This fact limits the usefulness of the 87Sr/86Sr parameter as a tracer in water studies within the basin.