## 3 Factors Governing Survival and Occurrence of Opportunistic Pathogens in Premise Plumbing Systems
### Challenges Inherent to the Current Water Treatment Paradigm  
The current water treatment doctrine originates from the need to combat waterborne pathogens such as _Salmonella_, _Escherichia coli_, and _Vibrio cholerae_, primarily from faecal contamination of supplies. The successful control of these disease-causing pathogens has been achieved and can be largely attributed to their natural attenuation over the time of exposure to drinking water, by treatment steps including disinfection, and because they do not multiply outside of their mammalian hosts. It has been established that in contrast, opportunistic premise plumbing pathogens are adapted to growth and persistence in drinking water, especially in building plumbing systems, and therefore tolerate disinfectant residuals. This explains why numbers of _Legionella pneumophilia_, _Mycobacterium avium_, and _Pseudomonas aeruginosa_, actually increase with distance from the treatment plant [13; 102]. [PERSON] et al. [2] describes the three main challenges that this poses to the current paradigm for water treatment. Firstly, it is believed that source tracking within a water distribution system is of limited value, since amplification and the likelihood of detection increases in remote parts of the system. Secondly, using disinfection guidance established for the eradication of _Escherichia coli_ can select for the prevalence of opportunistic pathogens by reducing competition for nutrients. Instead, new principals might be developed according to the susceptibility of these disinfect-resistant opportunistic pathogens. Lastly, locations for regulatory compliance sampling tend to be at the treatment plant effluent, which is the least likely place where opportunistic premise plumbing pathogens will be detected. Unfortunately, utilities are not obligated to sample stagnant water in buildings where detection is most likely [13; 15]. Table 7 summarises the additional problems associated with both traditional pathogens and OPPPs. There is evidently interplay, be it synergistic or antagonistic, amongst these various problems, which complicates risk assessment and management strategies. Most notably, direct conflicts exist between the control of OPPPs and the realisation of other public safety and sustainability goals (e.g., prevention of scaling and disinfection by-products, energy conservation, water conservation, and corrosion control). Fundamentals of conventional pathogen control that are transferable to the control of OPPPs include principles of disinfection, filtration, and public education. Beyond this, there is little overlap in regard to responsible parties and solutions. Although this paper previously highlighted the common characteristics of opportunistic premise plumbing pathogens, it is not realistic that one measure will reduce numbers of all species. In fact, it might never be practical or at all possible to completely eradicate all opportunistic pathogens from premise plumbing in homes, condominiumus, apartments, hospitals, and office buildings [13; 15]. Furthermore, it is not likely that control measures will have the same outcomes in treatment plants, distribution systems, and premise plumbing as conditions within and between systems vary widely. Therefore, case-specific strategies need to be adopted.