Opportunistic pathogens occurring in premise (i.e., building) plumbing systems, including strains of Legionella, Mycobacterium, Acanthamoeba, and Pseudomonas, are now frequently cited agents of waterborne disease outbreaks. Unlike traditional fecal pathogens, opportunistic pathogens are part of the drinking water microbial ecology and therefore require new paradigms for their control. With the onset of the "microbiome era", notions of eradicating all microbes in drinking water have proven unrealistic, making a probiotic concept worthy of consideration. Research is needed to better understand how engineering controls may individually, or in combination, select for a desirable microbiome, and how the microbiome itself may mediate proliferation of opportunistic pathogens. Ecological interactions such as competition, antagonism, and obligate parasite-host relationships offer potential targets for probiotic control of opportunistic pathogens. A probiotic approach may be defined as intentional inoculation of beneficial microbes or choosing conditions that select for a desirable microbiome. This critical review synthesizes the state of the knowledge of the factors governing opportunistic pathogen control in premise plumbing and potential opportunities for and barriers to implementation of a probiotic approach. Future effort is recommended to demonstrate the feasibility of the probiotic concept; to develop effective, practical, and safe protocols; and to engage relevant stakeholders in evaluating options and assessing corresponding risks.