Bacteria have been shown to live in "premises plumbing systems". The latter refers to the "pipes and fixtures within a building that transport water to taps after it is delivered by the utility". Community water systems have been known for centuries to spread waterborne diseases like typhoid and cholera, however "opportunistic premises plumbing pathogens" have been recognized only more recently; Legionella pneumophila discovered in 1976, Mycobacterium avium, and Pseudomonas aeruginosa are the most commonly tracked bacteria, which people with depressed immunity can inhale or ingest and may become infected with. These opportunistic pathogens can grow for example in faucets, shower heads, water heaters and along pipe walls. Reasons that favor their growth are "high surface-to-volume ratio, intermittent stagnation, low disinfectant residual, and warming cycles". A high surface-to-volume ratio, i.e. a relatively large surface area allows the bacteria to form a biofilm, which protects them from disinfection.
Plumbers in Australia have licensing requirements that differ from state to state but it is generally accepted a 4-year apprenticeship with a further minimum experience of 2 years (6 years total) and a further curricular requirement as a benchmark for licensing. Licensed plumbers are also expected to maintain minimum relevant training requirements to maintain their plumbing license