The report presents an analysis of the costs and benefits of controlling microbiological contaminants in public water systems using surface water sources through the criteria specified in the final Surface Water Treatment Rule (SWTR). The analysis was prepared in compliance with Executive Order 12291 and the Regulatory Flexibility Act. A draft Regulatory Impact Analysis was prepared on September 1, 1987, in support of the proposed SWTR which was published in the Federal Register on November 7, 1987. The present document does not duplicate material presented previously. Instead, the document focuses on items which have changed in the analysis since the publication of the proposed rule, largely in response to public comments.