This research study was designed to evaluate chlorine dioxide disinfection as an alternative for drastically reducing or preventing the production of trihalomethanes that result during chlorination. Also, the effectiveness of virgin and reactivated granular activated carbon (GAC) for removal of organic compounds present in the source water as well as any formed after disinfection was investigated. The performance of 0.38 cu m/minute (100 gallon per minute) pilot plant with pre and post chlorine dioxide disinfection and two parallel post-adsorber GAC contactors was compared to a full-scale plant using chlorine disinfection without GAC adsorption. The parallel GAC contactors consisted of virgin in one contactor and reactivated GAC in the other one that were continuously operated and evaluated until exhaustion. After about 90 days of operation, the GAC was educted and reactivated off-site by an infrared furnace. Analysis performed during the project consisted of quantification of fourteen volatile and eight extractable organic compounds along with qualitative (detected/nondetected) determinations by mass spec scans of 32 additional volatiles and 54 extractable organics. Additional data were collected on nine inorganic metals, TOC, and other parameters such as turbidity, SPC and total coliforms.