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The Casitas Municipal Water District in Ventura County, California uses a surface water supply for drinking water while currently providing disinfection only. As a result of the Surface Water Treatment Rule (SWTR), Casitas will be required to implement filtration treatment. Although Casitas has excellent water quality with average raw water turbidities less than 1 NTU and very low coliforms and plate counts, it cannot meet all of the exemption criteria in the federal rule. In addition, the California Department of Health Services (CDHS) is developing its own SWTR which will require all surface water sources to filter with no exceptions. A treatment feasibility study recommended that an in-line filtration process (coagulation and filtration only) be used including ozone as a predisinfectant and chloramines as a residual disinfectant. This type of process is not an approved CDHS filtration process (i.e. conventional, direct, slow sand, or diatomaceous earth), so a pilot study was required to prove equivalency to one of the approved processes. This paper includes the methods and procedures used for the pilot study, the results obtained, and relevant conclusions. See more