We will let the Greater Cincinnati Water Works answer this question. In the Safe Drinking Water Report, they state:
"As water travels over the surface of the land or through the ground, it dissolves naturally occurring minerals and, in some cases, radioactive material, and can pick up substances resulting from the presence of animals or from human activity [sewage].
Contaminants that may be present in source water include: microbial contaminants, such as viruses and bacteria, which may come from sewage treatment plants, septic systems, agricultural livestock operations and wildlife; inorganic contaminants, such as salts and metals... pesticides and herbicides... organic chemical contaminants, including synthetic and volatile organic chemicals, which are byproducts of industrial processes and petroleum production... and radioactive contaminants, which can be naturally occurring or be the result of oil and gas production and mining activities."