Raw water pumped from the Mississippi River was clarified and fluoridated. A portion was taken through a high pressure and filter and split into five parallel streams at a pilot scale drinking water treatment plant. Four streams were each dosed with a different disinfectant (chlorine, monochloramine, chlorine dioxide, ozone). The fifth stream was without disinfection (control). All streams were further divided and passed through parallel granular activated carbon (GAC) columns or sand filter. The organic chemical analysis of each stream included total organic carbon (TOC), total organic halide (TOX) trihalomethanes, chlorinated hydrocarbons, alkanes, phthalates, chlorobenzenes, nitrobenzenes, and alkyladehydes. Ozonation and chlorination produced the most dramatic changes in several non-volatile organic concentrations. Trihalomethanes were the volatile organics most effected by disinfection (chlorination). Two thousand gallon water samples were collected and concentrated for toxicological testing. According to the Ames assay, GAC was effective in removing both the mutagenicity of chlorinated drinking water and the potential of water to become mutagenic when treated with chlorine. However, after 6-months use in the chlorine stream, the GAC was only partially effective in removing the mutagenicity of the water. Data indicated that with extended use (14-months), GAC may be ineffective in removing the mutagenicity of chlorinated water.