Building Plumbing Research Articles

AWWA Water Science Author Spotlight

Having recently published an article in AWWA Water Science, Christopher Douglas answered questions from the publication's editor-in-chief, Kenneth L. Mercer, about the research. Systematic Oversizing of Service Lines and Water Meters Christopher Douglas, Steven Buchberger, and Peter Mayer Currently I'm working as an assistant engineer at Hazen and Sawyer and progressing toward my Professional Engineer license rather than pursuing research as part of a group. I'm learning a lot about pumping water, assessment programs, and sewer and pipe rehabilitation. Christopher and his fiancée Adeline take a day hike outside of Colorado Springs, Colo. Christopher poses with his new-to-him bike. He's teaching himself how to replace the rear brake cable and looks forward to taking it out for a spin. I can think of a lot of teachers and mentors who have influenced me, but I'll answer this question with a shout-out to my graduate advisor, Dr. Steve Buchberger. We met each week to talk about my research and every week he had me prepare a one-page summary of my progress since the previous meeting. He was enthusiastic about the courses he taught and his research, but documenting my work throughout the entire project was an incredibly useful habit to build and something I try to maintain. I think it helps keep me focused on problems I'm capable of solving instead of going down rabbit holes. The civil engineering ethos says, “Design it a little bigger than you think it should be—after all, who knows what could happen,” which is sound advice. But this philosophy has drawbacks that are not often discussed. In addition to the cost of paying for something bigger than we need (e.g., a water meter), we're designing pumps and pipes to handle more flow than necessary. The method for sizing a building's plumbing system hasn't really been overhauled since the early 1940s, and we can come up with lower, more accurate peak flow estimates than could have been done back then. The effects of lowering the peak design flow ripple through a project to the cost of the meter, connection and service fees, pipe size, and sizing hydraulic equipment such as pumps inside the building. In the long term, it could be used to revise building codes. This would lead to lower building costs and energy costs in the form of smaller meters, pipes, pumps, and water heaters, as well as a better picture of how much water consumers use. I grew up, and live, in Ohio. Around here, some of our main issues related to water are aging infrastructure, pollution from surface runoff, and localized flooding, so right-sizing of water meters just isn't the first priority. Honestly, the research did more to influence my views on water than the other way around. I exercise and cook as much as I can. I recently began to garden and purchased a used road bike that I'm learning to maintain and ride—working with my hands has been a nice change of pace for me since so much of my life is academic. I like going for hikes and dog walks with my new fiancée, as well as reading and learning to code in Python. To learn more about Christopher's research, visit the article online at https://doi.org/10.1002/aws2.1165.

Data‐mining methods predict chlorine residuals in premise plumbing using low‐cost sensors

AbstractVariable water quality within buildings is of increasing concern due to public health impacts (e.g., lead, Legionella pneumophila, Naegleria fowleri, disinfection byproducts). Advances in data acquisition and analytics provide the opportunity to monitor real‐time building‐wide water quality variability. Accordingly, the goal of this research was to create a water quality sensor platform including data acquisition, storage, and mining methods able to monitor, and ultimately improve, water quality within buildings. The platform was used to monitor water temperature, pH, conductivity, oxidation–reduction potential, dissolved oxygen, and chlorine using sensors only. Other building data infrastructure, specifically Wi‐Fi logins by occupants, were used to approximate activity rates and associated water use. An advanced machine‐learning technique, gradient boosting machines, predicted the chlorine residuals throughout the building plumbing network better than multivariate linear regression models. Finally, the implications of water quality monitoring on costs, scalability, reliability, human dimensions, regulatory compliance, and future green building designs are considered.

Interactive Effects of Copper Pipe, Stagnation, Corrosion Control, and Disinfectant Residual Influenced Reduction of Legionella pneumophila during Simulations of the Flint Water Crisis.

Flint, MI experienced two outbreaks of Legionnaires’ Disease (LD) during the summers of 2014 and 2015, coinciding with use of Flint River as a drinking water source without corrosion control. Using simulated distribution systems (SDSs) followed by stagnant simulated premise (i.e., building) plumbing reactors (SPPRs) containing cross-linked polyethylene (PEX) or copper pipe, we reproduced trends in water chemistry and Legionella proliferation observed in the field when Flint River versus Detroit water were used before, during, and after the outbreak. Specifically, due to high chlorine demand in the SDSs, SPPRs with treated Flint River water were chlorine deficient and had elevated L. pneumophila numbers in the PEX condition. SPPRs with Detroit water, which had lower chlorine demand and higher residual chlorine, lost all culturable L. pneumophila within two months. L. pneumophila also diminished more rapidly with time in Flint River SPPRs with copper pipe, presumably due to the bacteriostatic properties of elevated copper concentrations caused by lack of corrosion control and stagnation. This study confirms hypothesized mechanisms by which the switch in water chemistry, pipe materials, and different flow patterns in Flint premise plumbing may have contributed to observed LD outbreak patterns.

Safety and Effectiveness of Monochloramine Treatment for Disinfecting Hospital Water Networks.

The formation of potentially carcinogenic N-nitrosamines, associated with monochloramine, requires further research due to the growing interest in using this biocide for the secondary disinfection of water in public and private buildings. The aim of our study was to evaluate the possible formation of N-nitrosamines and other toxic disinfection by-products (DBPs) in hospital hot water networks treated with monochloramine. The effectiveness of this biocide in controlling Legionella spp. contamination was also verified. For this purpose, four different monochloramine-treated networks, in terms of the duration of treatment and method of biocide injection, were investigated. Untreated hot water, municipal cold water and, limited to N-nitrosamines analysis, hot water treated with chlorine dioxide were analyzed for comparison. Legionella spp. contamination was successfully controlled without any formation of N-nitrosamines. No nitrification or formation of the regulated DBPs, such as chlorites and trihalomethanes, occurred in monochloramine-treated water networks. However, a stable formulation of hypochlorite, its frequent replacement with a fresh product, and the routine monitoring of free ammonia are recommended to ensure a proper disinfection. Our study confirms that monochloramine may be proposed as an effective and safe strategy for the continuous disinfection of building plumbing systems, preventing vulnerable individuals from being exposed to legionellae and dangerous DBPs.

Impacts of Municipal Water-Rainwater Source Transitions on Microbial and Chemical Water Quality Dynamics at the Tap.

When rainwater harvesting is utilized as an alternative water resource in buildings, a combination of municipal water and rainwater is typically required to meet water demands. Altering source water chemistry can disrupt pipe scale and biofilm and negatively impact water quality at the distribution level. Still, it is unknown if similar reactions occur within building plumbing following a transition in source water quality. The goal of this study was to investigate changes in water chemistry and microbiology at a green building following a transition between municipal water and rainwater. We monitored water chemistry (metals, alkalinity, and disinfectant byproducts) and microbiology (total cell counts, plate counts, and opportunistic pathogen gene markers) throughout two source water transitions. Several constituents including alkalinity and disinfectant byproducts served as indicators of municipal water remaining in the system since the rainwater source does not contain these constituents. In the treated rainwater, microbial proliferation and Legionella spp. gene copy numbers were often three logs higher than those in municipal water. Because of differences in source water chemistry, rainwater and municipal water uniquely interacted with building plumbing and generated distinctively different drinking water chemical and microbial quality profiles.

Feeding the Building Plumbing Microbiome: The Importance of Synthetic Polymeric Materials for Biofilm Formation and Management

The environmental conditions in building plumbing systems differ considerably from the larger distribution system and, as a consequence, uncontrolled changes in the drinking water microbiome through selective growth can occur. In this regard, synthetic polymeric plumbing materials are of particular relevance, since they leach assimilable organic carbon that can be utilized for bacterial growth. Here, we discuss the complexity of building plumbing in relation to microbial ecology, especially in the context of low-quality synthetic polymeric materials (i.e., plastics) and highlight the major knowledge gaps in the field. We furthermore show how knowledge on the interaction between material properties (e.g., carbon migration) and microbiology (e.g., growth rate) allows for the quantification of initial biofilm development in buildings. Hence, research towards a comprehensive understanding of these processes and interactions will enable the implementation of knowledge-based management strategies. We argue that the exclusive use of high-quality materials in new building plumbing systems poses a straightforward strategy towards managing the building plumbing microbiome. This can be achieved through comprehensive material testing and knowledge sharing between all stakeholders including architects, planners, plumbers, material producers, home owners, and scientists.

An investigation of spatial and temporal drinking water quality variation in green residential plumbing

Drinking water chemical quality can deteriorate after water enters building plumbing. This study aimed to better understand seasonal and spatial water quality differences in a highly monitored net-zero energy residential building. Water flow rate and temperature were monitored for one year at the service line and at every fixture throughout the crosslinked polyethylene plumbing. Discrete water sampling events (58) were conducted at the service line, 1st floor kitchen sink, 2nd floor bathroom sink, the water heater, and 2nd floor shower. More than 2.4 billion online monitoring records were collected for fixture flow and temperature. In-building water stagnation time varied seasonally and across fixtures. Significant spatial and temporal water chemical quality variations were found. Average seasonal variability was found for service line temperature (15–23 °C) for the total chlorine residual (0.4–0.9 mg/L-Cl2), NH3 (<0.01–0.4 mg/L-N), NO3− (0.1–0.8 mg/L-N), and Cu (32–81 μg/L) concentrations. For 10.3% of the discrete water sampling events, service line water did not contain a detectable total chlorine residual. Water pH consistently and significantly increased in the plumbing system from 7.5 to 9.4, and total trihalomethane (TTHM) levels increased up to 89%. The service line total organic carbon level (0.5–0.6 mg/L) was consistent, but much greater in-building variability was found for cold (0.4–61.0 mg/L) and hot water (0.5–4.7 mg/L). Models are needed to predict chemical water quality at the faucet using service line water quality results and plumbing design and operational information. Building water sensor technology innovations are also needed.

Identification of Factors Affecting Bacterial Abundance and Community Structures in a Full-Scale Chlorinated Drinking Water Distribution System

Disentangling factors influencing suspended bacterial community structure across distribution system and building plumbing provides insight into microbial control strategies from source to tap. Water quality parameters (residence time, chlorine, and total cells) and bacterial community structure were investigated across a full-scale chlorinated drinking water distribution system. Sampling was conducted in treated water, in different areas of the distribution system and in hospital building plumbing. Bacterial community was evaluated using 16S rRNA gene sequencing. Bacterial community structure clearly differed between treated, distributed, and premise plumbing water samples. While Proteobacteria (60%), Planctomycetes (20%), and Bacteroidetes (10%) were the most abundant phyla in treated water, Proteobacteria largely dominated distribution system sites (98%) and taps (91%). Distributed and tap water differed in their Proteobacteria profile: Alphaproteobacteria was dominant in distributed water (92% vs. 65% in tap waters), whereas Betaproteobacteria was most abundant in tap water (18% vs. 2% in the distribution system). Finally, clustering of bacterial community profiles was largely explained by differences in chlorine residual concentration, total bacterial count, and water residence time. Residual disinfectant and hydraulic residence time were determinant factors of the community structure in main pipes and building plumbing, rather than treated water bacterial communities.

Analysis of building plumbing system flushing practices and communications.

Drinking water distribution system contamination incidents can prompt public agencies and drinking water utilities to issue do-not-drink and do-not-use advisories. After the contaminant is cleared from distribution mains, consumers are often directed to flush their plumbing. However, little validated guidance and few evaluated communications strategies are available on using flushing to decontaminate building water systems. Additionally, limited data support the effectiveness of current practices and recommendations. In this study, expert elicitation was used to assess existing flushing guidance and develop validated flushing guidance and communications for single-family residences. The resulting guidance recommends progressively opening all cold-water taps from the closest to point of entry to the furthest and allowing the water to run for at least 20 minutes. Hot-water taps should be opened progressively and run for at least 75 minutes. The guidance language and format conformed to grade-level and readability scores within recommended health communication ranges. The readability of eight other flushing guidance documents was also evaluated for contamination incidents from 2008-2015. Seven were written at a 10th-12th grade level, above the 6th-7th grade level recommended for health communications.

Review: Occurrence of the pathogenic amoeba Naegleria fowleri in groundwater

Naegleria fowleri is a thermophilic free-living amoeba found worldwide in soils and warm freshwater. It is the causative agent of primary amebic meningoencephalitis, a nearly always fatal disease afflicting mainly children and young adults. Humans are exposed to the organism via swimming, bathing, or other recreational activity during which water is forcefully inhaled into the upper nasal passages. Although many studies have looked at the occurrence of N. fowleri in surface waters, limited information is available regarding its occurrence in groundwater and geothermally heated natural waters such as hot springs. This paper reviews the current literature related to the occurrence of N. fowleri in these waters and the methods employed for its detection. Case reports of potential groundwater exposures are also included. Despite increased interest in N. fowleri in recent years due to well-publicized cases linked to drinking water, many questions still remain unanswered. For instance, why the organism persists in some water sources and not in others is not well understood. The role of biofilms in groundwater wells and plumbing in individual buildings, and the potential for warming due to climate change to expand the occurrence of the organism into new regions, are still unclear. Additional research is needed to address these questions in order to better understand the ecology of N. fowleri and the conditions that result in greater risks to bathers.

Impact of water heater temperature setting and water use frequency on the building plumbing microbiome

Hot water plumbing is an important conduit of microbes into the indoor environment and can increase risk of opportunistic pathogens (for example, Legionella pneumophila). We examined the combined effects of water heater temperature (39, 42, 48, 51 and 58 °C), pipe orientation (upward/downward), and water use frequency (21, 3 and 1 flush per week) on the microbial composition at the tap using a pilot-scale pipe rig. 16S rRNA gene amplicon sequencing indicated that bulk water and corresponding biofilm typically had distinct taxonomic compositions (R2Adonis=0.246, PAdonis=0.001), yet similar predicted functions based on PICRUSt analysis (R2Adonis=0.087, PAdonis=0.001). Although a prior study had identified 51 °C under low water use frequency to enrich Legionella at the tap, here we reveal that 51 °C is also a threshold above which there are marked effects of the combined influences of temperature, pipe orientation, and use frequency on taxonomic and functional composition. A positive association was noted between relative abundances of Legionella and mitochondrial DNA of Vermamoeba, a genus of amoebae that can enhance virulence and facilitate replication of some pathogens. This study takes a step towards intentional control of the plumbing microbiome and highlights the importance of microbial ecology in governing pathogen proliferation.

Educational building conditions and the health of users

In order to maintain a healthy learning environment, diagnosis and management of defects in the educational facility are paramount. The preliminary results of the ongoing research reported here seek to identify defects associated with educational buildings and their effects on the health of polytechnic students and staff in Nigeria. A questionnaire survey, including 34 defects based on a post-occupancy evaluation (POE) was used to establish relationships with the health of polytechnic students and staff. Two hundred (200) respondents were randomly selected based on their schools (faculty) within Lagos State Polytechnic. Descriptive and inferential statistics were used for analysis of the collected data. The results of the study indicate that defects such as plumbing and dampness problems, cobwebs and dust, are prominent in the institution. Also the relationship between building conditions (defects) and health problems was established, with the predictors of the health problems. Based on the findings, it is important for designers and managers of facilities within tertiary institutions to develop and implement design and maintenance policies targeted at minimizing the likelihood of plumbing, dampness, electrical, cobweb and dust problems in educational buildings due to the health risks induced by the defects. It is evident that effective maintenance schedules and policies should be put in place to ensure that facilities are not left to decay before replacement.

The water watchdog.

Water treatment and corrosion expert Marc Edwards made headlines recently for his work to uncover and address the elevated lead levels in drinking water in Flint, Michigan. Edwards says he originally chose to become an environmental engineer because it “sounded like a great, altruistic career.” Altruism has led the professor at Virginia Polytechnic Institute and State University in Blacksburg to some risky professional decisions. He has taken on the U.S. Centers for Disease Control and Prevention and the Environmental Protection Agency for failing to intervene effectively in Flint and, a decade earlier, in Washington, D.C., when it was experiencing its own water crisis. This interview has been edited for clarity and brevity. ![Figure][1] ILLUSTRATION: ROBERT NEUBECKER > “It's about seeing something that's wrong and being unwilling to accept it.” Q: Why did you pursue water safety research? A: What gives me joy is creating new knowledge, especially knowledge that helps normal people. I've always gravitated toward the work that had the biggest real-world impacts and was being overlooked. My research on building plumbing systems has profound health and economic implications, but no one wanted to take responsibility for the issue. Q: When you've discovered problems, how have you gotten them addressed? A: Science by itself is powerless when you're dealing with government agencies. I had to cross the line and become an activist, filing Freedom of Information Act requests and working with politicians and people on the ground. You have to reach this critical mass where you can put enough pressure on these agencies to make them take action, and you will never do that with science alone. If you're not going to fight to the bitter end, don't get started. You have to decide: Are you willing to do whatever it takes to see this through, and can you accept the likelihood that you are going to fail? The odds are against you. I'm one of the lucky ones. It makes me feel so humble to think about all of those who put their professional lives on the line and whose careers were destroyed. Q: How do your colleagues view your activism? A: I engage in activism as a last resort, after every scientific path has failed. Since I personally find activism distasteful, I forgive the academics who also view it negatively. The majority of my colleagues are indifferent or bemused, focused on their own problems and getting their next research dollar. Q: How does the current academic culture affect research like yours? A: We have to address the pressures to publish and get funding so that we can ask ourselves whether our research is doing good for the world. I'm very fearful of the perverse incentives of academia right now. We spend all our time sucking up to funding agencies. We're all such cowards—and with good reason, because the system does not reward good heroic actors. At the same time, because cowardice is the norm, it creates a tremendous opportunity for those who want to go this path, because no one else is doing it and there is so much injustice. We are still attracting some great people who I firmly believe are ethical, altruistic scientists, but at some point they might become the minority. My biggest fear is that the culture of academia is going to get to the point where these scientists ask, “Can I have a career without cutting corners or cheating?” I don't want us to get to the point where I might have to tell young people, “I'm not sure that you can.” Q: What motivates you to carry on despite the challenges? A: I am the most optimistic person in the world. You have to be optimistic to think that you can change things. It's not blind optimism; it's about seeing something that's wrong and being unwilling to accept it. You have to say, “I'm going to fight to make this world a better place.” And you have to make sure that the world doesn't change you. It's only the people that the world doesn't change who are going to change the world. [1]: pending:yes

Biofilms in shower hoses – choice of pipe material influences bacterial growth and communities

Flexible polymeric pipe materials are commonly used as shower hoses or connections to faucets in the last meters of building plumbing, but these tend to leach high concentrations of carbon that encourage bacterial growth.

Prevalence of Legionella in premise plumbing in Hungary

Legionella is one of the emerging concerns of water quality in built water environments. Premise plumbing systems are among the recognised sources of infection. In the present study, colonisation of hot water networks in health care facilities, schools, hotels, private residences, office and industrial buildings was investigated. Data was analysed in connection with building and premise plumbing characteristics. Over 60% of all buildings were colonised by Legionella; counts were over 1000 CFU/L in 49%. The most prevalent type was Legionella pneumophila serogroup 2–14, isolated from 75% of the positive samples. Centrally produced hot water was found to be a key risk factor (46% of the samples were positive vs. 16% in individual systems); within this group the type of the building was less relevant. Colonisation levels in schools were similar to hotels or hospitals, representing a previously underestimated risk setting. Systems supplied by water from deep groundwater sources were significantly less likely to be colonised than more vulnerable sources (bank-wall filtration, surface water abstraction or karstic water; 28% vs. 51% positive), regardless of the type of treatment applied, including the presence of disinfection. The aggravating effect of larger, more complex and older buildings on colonisation was also confirmed.The present study represents the first baseline analysis, pre-empting regulation or monitoring requirements for Legionella. The prevalence of legionellae and the identified risk factors are indicative for other settings lacking targeted interventions. The statistically confirmed risk factors can serve as indicators for preliminary risk assessment and the prioritisation of interventions.

Impact of Water Chemistry, Pipe Material and Stagnation on the Building Plumbing Microbiome.

A unique microbiome establishes in the portion of the potable water distribution system within homes and other buildings (i.e., building plumbing). To examine its composition and the factors that shape it, standardized cold water plumbing rigs were deployed at the treatment plant and in the distribution system of five water utilities across the U.S. Three pipe materials (copper with lead solder, CPVC with brass fittings or copper/lead combined pipe) were compared, with 8 hour flush cycles of 10 minutes to simulate typical daily use patterns. High throughput Illumina sequencing of 16S rRNA gene amplicons was employed to profile and compare the resident bulk water bacteria and archaea. The utility, location of the pipe rig, pipe material and stagnation all had a significant influence on the plumbing microbiome composition, but the utility source water and treatment practices were dominant factors. Examination of 21 water chemistry parameters suggested that the total chlorine concentration, pH, P, SO4 2- and Mg were associated with the most of the variation in bulk water microbiome composition. Disinfectant type exerted a notably low-magnitude impact on microbiome composition. At two utilities using the same source water, slight differences in treatment approaches were associated with differences in rare taxa in samples. For genera containing opportunistic pathogens, Utility C samples (highest pH of 9–10) had the highest frequency of detection for Legionella spp. and lowest relative abundance of Mycobacterium spp. Data were examined across utilities to identify a true universal core, special core, and peripheral organisms to deepen insight into the physical and chemical factors that shape the building plumbing microbiome.

Surveillance for Waterborne Disease Outbreaks Associated with Drinking Water - United States, 2011-2012.

Advances in water management and sanitation have substantially reduced waterborne disease in the United States, although outbreaks continue to occur. Public health agencies in the U.S. states and territories* report information on waterborne disease outbreaks to the CDC Waterborne Disease and Outbreak Surveillance System (http://www.cdc.gov/healthywater/surveillance/index.html). For 2011-2012, 32 drinking water-associated outbreaks were reported, accounting for at least 431 cases of illness, 102 hospitalizations, and 14 deaths. Legionella was responsible for 66% of outbreaks and 26% of illnesses, and viruses and non-Legionella bacteria together accounted for 16% of outbreaks and 53% of illnesses. The two most commonly identified deficiencies† leading to drinking water-associated outbreaks were Legionella in building plumbing§ systems (66%) and untreated groundwater (13%). Continued vigilance by public health, regulatory, and industry professionals to identify and correct deficiencies associated with building plumbing systems and groundwater systems could prevent most reported outbreaks and illnesses associated with drinking water systems.

Release of drinking water contaminants and odor impacts caused by green building cross-linked polyethylene (PEX) plumbing systems

Green buildings are increasingly being plumbed with crosslinked polyethylene (PEX) potable water pipe. Tap water quality was investigated at a six month old plumbing system and chemical and odor quality impacts of six PEX pipe brands were examined. Eleven PEX related contaminants were found in the plumbing system; one regulated (toluene) and several unregulated: Antioxidant degradation products, resin solvents, initiator degradation products, or manufacturing aides. Water chemical and odor quality was monitored for new PEX-a, -b and -c pipes with (2 mg/L free chlorine) and without disinfectant over 30 days. Odor and total organic carbon (TOC) levels decreased for all pipes, but odor remained greater than the USA's Environmental Protection Agency's (USEPA) secondary maximum contaminant level. Odors were not attributed to known odorants ethyl-tert-butyl ether (ETBE) or methyl-tert-butyl ether (MTBE). Free chlorine caused odor levels for PEX-a1 pipe to increase from 26 to 75 threshold odor number (TON) on day 3 and affected the rate at which TOC changed for each brand over 30 days. As TOC decreased, the ultraviolet absorbance at 254 nm increased. Pipes consumed as much as 0.5 mg/L as Cl2 during each 3 day stagnation period. Sixteen organic chemicals were identified, including toluene, pyridine, methylene trichloroacetate and 2,4-di-tert-butylphenol. Some were also detected during the plumbing system field investigation. Six brands of PEX pipes sold in the USA and a PEX-a green building plumbing system impacted chemical and drinking water odor quality.

Probiotic Approach to Pathogen Control in Premise Plumbing Systems? A Review

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.

Ecology of Nontuberculous Mycobacteria—Where Do Human Infections Come from?

Nontuberculous mycobacteria (NTM) are environmental, opportunistic human pathogens whose reservoirs include peat-rich potting soil and drinking water in buildings and households. In fact, humans are likely surrounded by NTM. NTM are ideally adapted for residence in drinking water distribution systems and household and building plumbing as they are disinfectant-resistant, surface adherent, and able to grow on low concentrations of organic matter. For individuals at risk for NTM infection, measures can be taken to reduce NTM exposure. These include avoiding inhalation of dusts from peat-rich potting soil and aerosols from showers, hot tubs, and humidifiers. A riskanalysis of the presence of NTM in drinking water has not been initiated because the virulence of independent isolates of even single NTM species (e.g., Mycobacterium avium) is quite broad, and virulence determinants have not been identified.