In April 1985, the American Water Works Association Research Foundation (AWWA), under a grant from the U.S. Environmental Protection Agency (EPA), Office of Drinking Water, convened a workshop in Baltimore, Maryland, to discuss options for regulating microbial contaminants, and treatment requirements such as filtration and disinfection. The primary objectives of the workshop were to provide EPA with advice and detailed comments and recommendations on (1) specific monitoring requirements for coliforms, turbidity, heterotrophic bacteria, viruses, and Giardia, (2) definitions of filtration and disinfection for regulatory purposes, and (3) appropriate variance criteria for the treatment technique regulations (filtration and disinfection of surface waters and disinfection of ground waters).