Microbiology of household plumbing causes and consequences
Drinking water, even when distributed safely, deteriorates in quality after entering the home. The microbiological quality of this building plumbing water is of particular interest because opportunistic pathogens (e.g. Legionella pneumophila) are known to proliferate there. Beyond the potential threat to health, microbial growth results in customer complaints about taste, odor, color, turbidity, slime formation, and filter clogging in building plumbing.
While water distributors strive to deliver a product that remains stable in the home, they have minimal influence on the design, maintenance, and operation of building plumbing systems. At the property line, legal responsibility for the water shifts away from the water distributor to the building owner. On top of this, monitoring water stability in the home requires invasive sampling and has potential privacy implications. All of these factors contribute to a poor understanding of the microbiology of water in building plumbing.
Many factors give building plumbing a unique growth environment. Pipe materials are varied and sometimes unregulated. In the building multiple materials are found within inches of each other. With high surface area to volume ratios, and more frequent replacement (e.g. with bathroom remodels), these materials have a considerably higher impact in buildings than in the distribution network. Temperature is high (e.g. hot and mixed water distribution) compared to the distribution network, creating favorable growth conditions. Building distalends are also only flowing intermittently (i.e. long stagnation times), allowing for biofilm and water phase interactions. While all of these factors are known to contribute to growth, their impact on bacterial concentration and composition is not completely understood. Moreover, each building is different with respect to design, operation, and location, complicating synthesis of various building plumbing studies.
The research presented here primarily addresses three factors in building plumbing, namely material quality, stagnation, and temperature. These three factors come together at shower hoses, which have (1) flexible polymeric materials that leach large amounts of biodegradable carbon, (2) long stagnation intervals (i.e. once daily showers), and (3) temperatures ranging only from warm to room temperature (i.e. neither hot nor cold). Shower hoses were thus often used as a model system throughout this thesis, for studies of both biofilm development and stagnation dependent water dynamics. As this research was supported by highly quantitative culture-independent methods (i.e., flow cytometry and qPCR), some critical aspects of these methods were also further investigated.
Throughout this work, building plumbing is approached as an ecological system governed by simple ecological principles, primarily that of dispersal (i.e., movement of bacteria) and selection (i.e., favorable growth conditions). This approach allowed for a cohesive understanding of building plumbing behavior in both large data sets from around the world and a series of highly controlled systems. For example, the quality of polymeric material was selective, but the effect could be surpassed by dispersal from the distribution network, and the selective factors ‘upstream’, like chlorination or temperature. During stagnation, spatial dispersal along the continuum of water delivery was insignificant compared to local dispersal from the biofilm to the water phase, which affected both concentration and microbiome composition. Ultimately, controlling bacterial growth in buildings will take advantage of these principles, and will furthermore embrace the inevitable growth in building plumbing pipes and water. Altogether, this research presents valuable steps towards a better understanding and better management of the microbiology within building plumbing.