This Webcast presented information on the state of the science of opportunistic pathogens in premise plumbing (OPPPs) based on a WaterRF report and Expert Workshop (project #4379). The Webcast focused on five model OPPPs: Legionella pneumophila, Mycobacterium avium Complex (MAC), Pseudomonas aeruginosa, Acanthamoeba spp., and Naegleria fowleri. Current understanding of their epidemiology, microbial ecology, methodology, and engineering controls was discussed.