In spring 2020, reduced water demand was an unintended consequence of COVID-19 pandemic-related building closures. Concerns arose that contaminants associated with water stagnation, such as Legionella pneumophila, could become prevalent. To investigate this potential public health risk, samples from 26 reduced-occupancy buildings across 11 cities in the United States, Canada, and Switzerland were analyzed for L. pneumophila using liquid culture (Legiolert, n=258) and DNA-based methods (qPCR/ddPCR, n=138). L. pneumophila culture-positivity was largely associated with just five buildings, each of which had specific design or operational deficiencies commonly associated with L. pneumophila occurrence. Samples from free chlorine buildings had higher culture-positivity (37%) than chloramine buildings (1%), and 78% of culture-positive samples occurred when the residual was [≤]0.1 mg/L Cl2. Although overall sample positivities using culture- and DNA-based methods were equivalent (34% vs. 35%), there was disagreement between the methods in 13% of paired samples. Few buildings reported any water management activities, and L. pneumophila concentrations in flushed samples were occasionally greater than in first-draw samples. This study provides insight into how building plumbing characteristics and management practices contribute to L. pneumophila occurrence during low water use periods and can inform targeted prevention and mitigation efforts.

Synopsis StatementLegionella pneumophila occurrence was evaluated in reduced-occupancy buildings during the COVID-19 pandemic across multiple cities.

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Legionella pneumophila occurrence in reduced-occupancy buildings in 11 cities during the COVID-19 pandemic

COVID-19 shutdowns drastically increased the frequency and duration of water stagnation events in building plumbing systems, urging local authorities to issue guidance for the safe reopening of buildings mostly by recommissioning flushing. The objectives of this study were to document the dynamic changes of bacterial indicators [adenosine triphosphate (ATP), total and intact cell counts (TCC, ICC)] and the prevalence of Legionella pneumophila (Lp) in 20–21 showerheads in a large building before (16-week building closure) and then shortly (24 h) and monthly (4-week of distal water stagnation) after targeted recommissioning flushing. Following the 16-week shutdown, the highest mean of ATP (10 pg ATP/mL), TCC (1.7 × 106 count/mL) and ICC (5.2 × 105 count/mL) were measured in first draw samples. This bacterial amplification was mostly attributable to detachment from biofilm present in the distal devices and immediate connecting piping. Culture-based (mean of 4 487 MPN/L) and quantitative polymerase chain reaction (qPCR; mean of 63 822 gu/L) concentrations of Lp were respectively measured in 81 and 90% of first draw samples. Individual flushing of showerheads for 5 min resulted in 1.2–278-fold decreases in ATP, whereas TCC and ICC were lowered by 1.1- and 0.7-log on average. A one-log reduction in culture-based and qPCR Lp was only achieved in 63 and 29% of paired water samples, resulting in less than one-log reduction in mean risk values per exposure, thus demonstrating the limited effects of fixture-flushing for risk reduction. Clear short-term (24 h) benefits of device recommissioning flushing included lowered values of all bacterial indicators and Lp levels systematically under the common alert threshold of 1 000 MPN/L in first draws. However, after a period of 1 month without water use, these benefits were mostly lost with considerable rebounds of concentrations to similar levels than those measured following the 16-week building closure. Results highlight the temporary benefits of device recommissioning flushing for the control of Lp in shower systems, especially in buildings colonized by Legionella.

/pdf/impact-of-recommissioning-flushing-on-legionella-pneumophila-1xpq7ljn.pdf

Impact of recommissioning flushing on Legionella pneumophila in a large building during the COVID-19 pandemic

Introduction Legionella pneumophila is an opportunistic pathogen that is a key contributor to drinking water-associated disease outbreaks in the United States. Prolonged water stagnation periods in building plumbing systems due to low occupancy, especially during building shutdowns, breaks, and holidays, can lead to water quality deterioration and (re)colonization of buildings with L. pneumophila. Water monitoring in buildings typically relies on grab samples with small datasets. Methods In this study, a larger dataset was created by sampling a Leadership in Energy and Environmental Design (LEED)-certified data-rich commercial building for L. pneumophila and physical-chemical water quality during the COVID-19 pandemic after reduced building occupancy. A proxy for human occupancy rates using WIFI logins was recorded throughout the study period. Results L. pneumophila was observed in grab samples taken throughout the building, where concentrations generally increased with greater distances from the building point of entry to locations throughout the building. Factors conducive to microbial growth were identified in the building including fluctuations in water temperatures, lack of chlorine residual, a low water heater setpoint, colonized water-saving fixtures, prolonged stagnation throughout the building; especially in an expansion tank designed to reduce pressure issues during demand fluctuations, and the presence of oversized softener tanks with ion exchange resin that contributed to chlorine residual removal as well as colonization of the resin with L. pneumophila. Discussion Flushing and thermal disinfection alone did not resolve the problem, and replacement of the expansion tank ultimately resolved the L. pneumophila issue. As ad-hoc approaches are logistically- and time-intensive, more proactive approaches are needed for informing preventative and corrective actions for reducing the risk of exposure to opportunistic pathogens in the building plumbing. Graphical Abstract Summary of water sampling locations and water quality parameters monitored.

/pdf/pinpointing-drivers-of-widespread-colonization-of-legionella-2ph4w07m.pdf

Pinpointing drivers of widespread colonization of Legionella pneumophila in a green building: Roles of water softener system, expansion tank, and reduced occupancy

Predicting heterotrophic plate count exceedance in tap water: A binary classification model supervised by culture-independent data.

Commercial and institutional buildings now experience weeks and even months with below‐normal occupancy due to remote work/learning, which results in reduced water use and has the potential to adversely impact water quality. This study monitored the variations in water quality in multiple university buildings during several months of below‐normal occupancy followed by several months of normal occupancy. The levels of free chlorine, copper, and cellular ATP in water varied within buildings and between buildings. Using Wi‐Fi activity as a surrogate for building occupancy, the free chlorine concentration in water increased as Wi‐Fi counts increased. The copper concentration in building water was higher when the occupancy was below‐normal compared with normal occupancy, and the copper concentration decreased as Wi‐Fi counts increased. Throughout the study, flushing a fixture at the time of use decreased the concentrations of copper and cellular ATP and increased the concentration of free chlorine.

Shift to remote learning degrades water quality in buildings

The role of water stagnation (~60 hours) in a 2-story commercial office building on building water quality was studied (January to February 2020) for three weekends. Chemical and biological parameters including pH, total chlorine, metals concentrations, Legionella spp. and total cell count were analyzed to understand the differences in water quality at the building entry point, and at eleven fixtures within the building’s copper plumbing. Consistently, the total chlorine concentration decreased over the weekend (p < 0.05), was greatest at the building entry point (maximum 0.8 mg/L), and was lowest within the plumbing (maximum 0.28 mg/L). As expected, total cell count levels were much greater on Monday compared to Friday (p < 0.05) at every sampling point. Legionella spp. was found to be highest at the fixture with no use recorded during sampling. Throughout the building, copper and lead levels increased over the weekend (p < 0.05). Copper exceedances above the federal health-based drinking water limit (1.3 mg/L) were localized to four fixtures, branched from the same riser, that shared a pattern of variable use. Flushing was conducted at one location with consistent copper exceedances but 54 minutes were required to reach the public water supply. Flushing was not a viable copper remediation method as it would need to be repeated every 19 hours or require discarding more than 50 gallons before use. No prior water testing was conducted in the buildings’ life. The results suggest that water quality varies significantly over the week. This has implications for water testing plans and interpretation of data collected from buildings.

Over the weekend: Water stagnation and contaminant exceedances in a green office building

Safe drinking water remains a major global challenge, especially in rural areas where, according to UNICEF, 80% of those without access to improved water systems reside. While water, sanitation, and hygiene (WASH)-related diseases and deaths are common outcomes of unsafe water, there is also an economic burden associated with unsafe water. These burdens are most prominent in rural areas in less-developed nations. Slow sand filters (SSFs), or biological sand filters (BSFs), are ideal water treatment solutions for these low-resource regions. SSFs are the oldest municipal drinking water treatment systems and improve water quality by removing suspended particles, dissolved organic chemicals, and other contaminants, effectively reducing turbidity and associated taste and odor problems. The removal of turbidity and dissolved organic compounds from the water enables the use of low-cost disinfection methods, such as chlorination. While the working principles of slow sand filtration have remained the same for over two centuries, the design, sizes, and application of slow sand filters have been customized over the years. This paper reviews these adaptations and recent reports on performance regarding contaminant removal. We specifically address the removal of turbidity and microbial contaminants, which are of great concern to rural populations in developing countries.

/pdf/slow-sand-filters-for-the-21st-century-a-review-1m4ablqe.pdf

Sruthi Dasika

Papers

Over the weekend: Water stagnation and contaminant exceedances in a green office building

Slow Sand Filters for the 21st Century: A Review