Some chemicals, such as 2% butyric acid and 0.1% caprylic acid, were effective in killing 5 log CFU E. coli O157:H7 in rumen content-contaminated water; however, they are not practical treatments because of cost constraints and objectionable odors. We evaluated a variety of chemicals in combination at different concentrations for their effects on inactivation of E. coli O157:H7 within 20 min in water heavily contaminated with rumen content. Four different combinations were highly effective, and all contained acidic calcium sulfate, which is a highly acidic methylated calcium sulfate, and lactic acid (38).