It is generally acknowledged that a variety of problems affecting aesthetics, health, and corrosivity of potable water can arise during installation of building plumbing systems. These include 'blue water', microbial infestation, and rapid loss of disinfectant residual, among other things. Frequently cited causes of the problems include metallic fines left in the plumbing lines from deburring, cutting and product fabrication; solder flux residuals (water soluble and petroleum based flux); and solvents for CPVC. Mechanistically, some materials such as flux contain high chloride, high ammonia and cause low pH, which can increase the corrosivity of water held in the lines. Indirect effects are also suspected to be important. For example, ammonia from flux and organic carbon from flux or PVC solvents can spur microbial growth, which in turn can reduce pH or otherwise increase corrosivity. Recent work has also demonstrated that problems with lead leaching to water from brass in modern plumbing can actually be worse in PVC/plastic than in copper systems, if certain types of microbes such as nitrifiers proliferate and drop pH. Some of the problems initiated by construction practices can persist indefinitely, causing higher levels of lead and copper in water, or longer term, contributing to failures of the plumbing system. Blue water from high copper concentrations is a confounding problem that continues to arise in some locales of the United States. One public elementary school in Miami Dade County is experiencing blue water issues as manifested by blue ice cubes and sink staining. In addition to the aesthetic problems, copper levels are above the EPA's Copper Action Level of 1.3 ppm. Bottled water has been substituted for tap water consumption, which has created a financial burden. The pH of the school's water ranges from 7.15 - 7.5 and the school itself is located 1 ½ miles off the main distribution line resulting in a very low chlorine residual of between 0.06 mg/L Cl2 and 0.18 mg/L Cl2. On site water was shipped to Virginia Tech from Miami to be used in this study. Preliminary testing showed that an increase in the pH of the water would decrease copper leaching. Several pH's were tested which revealed that increasing the pH of the water to 8.5 would drop copper below 1.3 mg/L. When these recommendations were implemented at the school, the high alkalinity and calcium rich water caused calcite scales to form which clogged the chemical feed nozzles. Further bench scale testing indicated that adding 2 mg/L orthophosphate corrosion inhibitor would effectively decrease copper to a level that would comply with the EPA's Copper Action Limit. Orthophosphate corrosion inhibitors are used by utilities to limit lead and copper corrosion from consumer's plumbing. An evaluation comparing the effects of both 100% orthophosphate inhibitor and orthophosphate/polyphosphate inhibitor blends was performed to study the effects they have on galvanic corrosion, metallic corrosion, microbial growth and the decay of chloramine disinfectant. On site water was sent to Virginia Tech from UNC for use in this bench scale study. The results from this study indicated that 100% orthophosphate inhibitor was the most effective corrosion inhibitor at decreasing metallic corrosion. It has long been known that microbial activity can have significant effects on water quality. This study evaluated nitrifying and heterotrophic bacterial growth in water systems containing copper pipes, a common plumbing product, and flux which is used in soldering copper pipes together in new construction. There are several types of commercially available fluxes which are often used when soldering new pipes together. Flux ingredients vary and can include extremely high concentrations of ammonia, zinc, chloride, tin, copper and TOC. Flux containing high amounts of ammonia can be detrimental to water quality because it can accelerate the occurrence of nitrification, thus creating a cascading set of problems including, but not limited to, pH decrease and copper corrosion. The results from this case study indicated that flushing a pipe system can effectively decrease the high concentrations of flux present in a new construction system; however, high levels of ammonia from flux can create an environment in which nitrifiers may proliferate within the system. Many water utilities in the United States are switching disinfection type from chlorine to chloramine due to the increased stability, longer residual time, and overall safety benefits of chloramine. Although chloramines have been found to be a desirable means for disinfection, chloramine decay is an issue of great concern because if the chloramine residual decays, it can leave a water system unprotected against microbial infestation. A preliminary examination of this issue was performed in a laboratory setting to evaluate the many components that effect the stability of chloramine decay, including alkalinity, phosphate, temperature, and various pipe materials. The results from this experiment revealed that temperature increase, pH increase, and aged tygon tubing all accelerated the rate of chloramine decay. / Master of Science

Opportunistic pathogens (OPs) can naturally colonize premise (i.e., building) plumbing and are the leading cause of disease associated with potable water in the U.S. and many other countries. While secondary disinfectant is added by utilities prior to water distribution through pipes, the residual in water at the property line is sometimes insufficient to suppress OP growth. Conditions encountered in premise plumbing can further diminish disinfectant in water after it crosses the property line. This dissertation examines how multiple factors at play in drinking water distribution systems and premise plumbing influence OP growth in order to inform development of rational guidance to reduce incidence of waterborne illness. Operating an at-scale cross-linked polyethylene (PEX) plumbing system with one water flush per day, influent chloramine always decayed within four hours in stagnant pipes containing mature biofilms, which is 2-3 orders of magnitude faster than in the same water not contacting pipes. Chloramine often followed second order decay kinetics, though decay rate coefficients were highly variable with some taps eventually transitioning from second to first order decay over time or with increasing influent chloramine concentration. The rate of chloramine decay was unexpectedly reduced in the water heater tank compared to room temperature pipes, possibly due to lower surface-area-to-volume ratio and higher temperature within the tank. A complementary glass jar experiment confirmed that, contrary to expectations, chloramine could decay slower at the higher temperature of 37-39°C maintained in the water heater, compared to the cooler 19-30°C typical of the pipes. These findings demonstrate the need for disinfectant decay models specific to conditions encountered in premise plumbing. Nitrification, a key microbial process that can catalyze chloramine decay, was typically complete within 24 hours after water entered the stagnant pipes. Counterintuitively, the water heater had a relatively lower rate of nitrification along with some detectable denitrification. This work also showed that oxygen, essential for aerobic microbial growth, can permeate through walls of PEX pipe and enter into the water from the atmosphere of the building. Considering the unique array of conditions that were found to influence the persistence of disinfectants in premise plumbing, a new approach was proposed for managing OP risk, referred to herein as the "CT framework." CT was defined as the integral of the chlorine concentration (C) at a point in the premise plumbing versus water retention time (T). Legionella pneumophila was not detectable in pipes with a CT > 78 mg*min/L over a 24 hour period, which is comparable to reported CT thresholds for 3-log inactivation of biofilm-associated L. pneumophila in batch experiments. There was a tradeoff between control of L. pneumophila and Mycobacterium avium in the water heater, as M. avium increased by >1 log as influent chloramine and CT increased, while L. pneumophila decreased by >1.5 logs. Further research is needed to elucidate the influence of factors such as water storage tank hydrodynamics and sediment on the persistence of different OPs. Building water retention time was also found to be an overarching variable that governs microbial growth in some circumstances in premise plumbing. Total cell counts and L. pneumophila occurrence mirrored expected trends based on the classic microbial growth curve with phases of lag, exponential growth, stationary growth, and decay. The location in the plumbing system where each phase dominated depended on water retention time, disinfectant level, and temperature. The microbial growth curve considerations add an additional dimension to the CT framework for predicting L. pneumophila growth potential in premise plumbing. Specifically, elevated heat or chloramine, was able to temporarily suppress or even eliminate growth, but the phases of classic microbial growth could be restarted once disinfectant or very high temperatures were absent. Total cell counts and L. pneumophila typically peaked at a building water retention time of 7 days, demonstrating that once a week flushing guidance to protect public health may not be advantageous in all situations. Collectively, this work offers fundamental and practical insights into factors driving disinfectant decay and microbial proliferation in premise plumbing, offering a modified CT and microbial growth concept framework to help guide the management of OPs in premise plumbing. / Doctor of Philosophy / Access to safe drinking water is fundamental to human health and wellbeing and is considered to be a human right by some agencies. Opportunistic pathogens (OPs) can grow in some drinking water systems and cause deadly diseases, such as Legionnaires' Disease. Legionnaires' Disease and illnesses caused by other OPs are now the leading cause of drinking water-associated disease in the U.S. and many other countries. Chlorine or chloramine are disinfectants required to be present in treated drinking water in the U.S. before it is piped through the distribution systems to consumers. This helps to limit growth of OPs and other microbes in the distribution systems. However, the concentration of disinfectant that remains in water as it crosses the property line is sometimes inadequate to suppress OP growth. Even if the amount of disinfectant entering a building is boosted, there are some plumbing materials and circumstances that can quickly reduce the disinfectant. These challenges are sometimes worsened by water and energy conservation efforts, which extend the time water spends in a building and presents tradeoffs with preventing OP growth. This dissertation examines how multiple factors at play in drinking water distribution systems and building plumbing individually and collectively influence OP growth, with a goal of developing rational guidance to reduce incidence of waterborne illness. Experiments were conducted using a large at-scale building plumbing system. These experiments revealed new insights into the relationship among factors such as how long the water stagnates in pipes, water temperature, the disinfectant concentration at each tap, and the level of specific OPs of concern. Chloramine was gone within four hours of stagnation in plastic cross-linked polyethylene (PEX) pipes containing a mature biofilm, which is 100-1000× faster than observed in the same water that did not contact pipes. The rate at which chloramine disappeared changed with conditions from tap to tap, or with time at a given tap, in ways that were unexpected based on prior assumptions. Further, the hydraulic characteristics and low temperature of the water heater influenced chloramine decay in the tank in a way that increased survival and release of OPs. We found that other microbes residing in pipes, such as nitrifying microbes, can also play a role in decay of disinfectant and their activity also is controlled by the water retention time and temperature in the system. These findings reinforce the need to thoroughly understand how chemical, biological, and hydraulic factors combine to influence OP growth in buildings. To account for the array of factors that contribute to the decay of disinfectant, we introduce premise plumbing "CT" as a new integrative framework to guide management of OPs. We define CT as the integral of the disinfectant concentration (C) at a stagnant point in the building plumbing verses the time (T) water has resided at that point, to characterize the ability of the water to kill or suppress growth of bacteria. If the calculated CT values in the at-scale plumbing system were high enough, Legionella pneumophila, the OP that causes Legionnaires' Disease, was never detected in pipes. However, if CT was too low, L. pneumophila was not controlled. Oddly, M. avium, another problematic OP, exhibited a contradictory trend within the water heater. This indicates that the CT concept may not control M. avium in chloraminated water heaters with complex water flow patterns and sediment. Higher chloramine caused lower L. pneumophila and higher M. avium in the water heater, but this tradeoff did not occur in cold water pipes when the room temperature was below that required for OP growth, indicating that room temperature setpoint could be a significant factor for OP control in buildings. Building water retention time, which is the time that water takes to move through the plumbing before it is consumed from a tap, was identified in this research to be a key driver of microbial growth that can be readily controlled by building managers. Trends of total microbial cell count and L. pneumophila in the premise plumbing system and complementary experiments followed all the phases of growth associated with bacteria in a simple glass jar, including a lag, rise, peak, and then decay of cells. Elevated heat or chloramine was able to temporarily suppress growth or even kill cells, but the phases of growth were again observed once the chemical or thermal disinfectant was removed. In any building, there is likely a frequency of flushing water at a given tap that is "worst case" for bacterial growth. In the absence of disinfectant, bacteria in pipes that are frequently supplied with nutrients through fresh water can be expected to have sustained growth, but if bacteria are starved of nutrients, there is some die off. In our system, total microbial cell counts and L. pneumophila peaked at a water retention time of about one week. Thus, this work suggests that current advice to flush building pipes once a week might sometimes create issues with microbial growth rather than solve them. Collectively, this research advances both fundamental and practical understanding of the factors driving disinfectant decay and microbial proliferation in premise plumbing. The premise plumbing CT and microbial growth concept framework is introduced to help inform better management of building water systems to prevent or remediate the growth of pathogens and reduce risk of human infection.