The Guidance Manual complements the filtration and disinfection treatment requirements for public water systems using surface water sources or ground water under direct influence of surface water as presented in the Surface Water Treatment Rule (SWTR). The manual provides guidance to Environmental Protection Agency Regional Offices, individual states and affected utilities in the implementation of the SWTR, and to help assure that actions taken toward implementation are consistent. The manual is advisory in nature and is meant to supplement the criteria of the SWTR. The guidance manual suggests design, operating and performance criteria for specific surface water quality conditions to provide the optimum protection from microbiological contaminants. Throughout the document, the term 'Primary Agency' refers to a State with primary enforcement responsibility for public water systems or 'primacy,' or to mean EPA in the case of a State that has not obtained primacy.