Four disinfectants commonly used in U.S. water treatment--chlorine, monochloramine, chlorine dioxide, and ozone--were applied to four parallel streams in a pilot plant in Jefferson Parish, La. Several organics, including surrogates such as total organic carbon and total organic halide, were evaluated to investigate the effects of disinfection and treatment by sand filtration and granular activated carbon (GAC) adsorption. Five toxicologic tests were also conducted to determine the general toxicity and the mutagenic-carcinogenic potential of disinfection of GAC adsorption. Results of the study showed that ozonation of clarified sand-filtered water produced fewer organics than the other disinfectants studied. The short-term animal toxicologic studies revealed difficulties in analyzing actual drinking waters for detectable toxic effects.