Conventional flushing is widely used to improve drinking water quality, yet its effectiveness in controlling opportunistic pathogens and nitrifiers in full-scale chloraminated drinking water distribution systems remains unclear. This study evaluated microbial and physicochemical responses to weekly flushing over four months at four sites in a chloraminated distribution system. Start-of-flush (SOF) and end-of-flush (EOF) samples were analyzed using heterotrophic plate counts, 16S rRNA gene sequencing, and qPCR targeting nontuberculous mycobacteria (NTM), ammonia-oxidizing bacteria (AOB), Nitrospira spp., and complete ammonia oxidizers (comammox). EOF samples had lower mean alpha diversity than SOF samples, with the observed richness decreasing by 35.4%. Flushing reduced mean heterotrophic plate counts by 0.63 log10 and mean NTM and nitrifier gene concentrations by 1.4-1.6 log10. These reductions coincided with lower mean turbidity levels (from 16.9 to 9.48 NTU), mean nitrite concentrations (from 0.14 to 0.050 mg/L NO2-N), and higher mean total chlorine levels (from 1.9 to 2.4 mg/L as Cl2). However, these effects were temporary, and repeated weekly flushing did not produce clear shifts in bulk water microbial community structure. Overall, conventional flushing provided short-term water quality improvements but did not achieve sustained reductions in persistent microbial populations.

Nitrification in chloraminated drinking water systems has been widely studied, although limited information is available on the role of biofiltration in shaping the nitrifier communities within drinking water distribution systems (DWDS). Additionally, the co-occurrence of comammox and canonical nitrifiers in drinking water systems remains unclear. This study investigates how biofiltration shapes nitrifier communities in a full-scale drinking water system where chloramine is a secondary disinfectant, and biofilters are backwashed with chloraminated water. Samples were collected monthly for one year from biofilter effluent, finished water, and three DWDS sites with varying water ages, water quality, and nitrite concentrations. Nitrifier abundances were quantified using droplet digital PCR, which showed contrasting temporal trends between the ammonia-oxidizing bacteria amoA gene and both nitrite-oxidizing bacteria 16S rRNA gene and comammox amoB gene abundances. Genome-resolved quantitative metagenomics revealed Nitrosomonas cluster 6a species, canonical Nitrospira species, and Nitrospira-like comammox species as the dominant nitrifiers. The same populations were detected in biofilter effluent and across DWDS sites, indicating that biofilter operation contributed to the persistence of nitrifiers in the DWDS. Further, DWDS site-specific factors, such as water age and disinfectant degradation, influenced the presence and abundance of individual nitrifier populations. These findings advance our understanding of how upstream treatment processes influence microbial community structure and nitrifier persistence in full-scale chloraminated DWDSs, and highlight the importance of considering biofilter operation, alongside disinfection practices, within integrated nitrification control strategies.

Drinking water opportunistic pathogens (OPs) and disinfection byproducts (DBPs) both pose risks to public health, and their variable occurrence from source to tap complicates efforts to control them simultaneously. Management of OPs and DBPs is further hindered by the historical division between microbial and chemical research. This review brings together the current knowledge regarding OPs and DBPs, identifies factors that influence the occurrence of both, and highlights areas where research is needed to better understand their health risks. First, we examine the current understanding of how OPs and DBPs are jointly influenced by physicochemical parameters, source water characteristics, treatment processes including disinfection, and distribution system properties. Temperature, for example, can affect OP and DBP occurrence, where higher temperatures can promote the growth of some OPs, such as Legionella pneumophila, but temperature's effect on DBPs is species-dependent. Methods for quantifying the risks associated with OPs (quantitative microbial risk assessment) and DBPs (chemical risk assessment) are compared, finding that the numerous assumptions and data gaps associated with each method limit comparability across contaminant types. We highlight the urgent need to fill existing data gaps and develop a more unified risk framework so as to move toward holistic assessment of microbial and chemical risks. This review provides suggestions for future research, highlighting ways that researchers might utilize established practices in OP or DBP studies to further our understanding of the other. For example, analysis of source water organic matter composition, which has advanced our understanding of DBP formation, could be utilized to elucidate how source water characteristics influence OPs. This review bridges the gap between the OP and DBP disciplines, arguing that collaboration between the two is needed to address the pressing challenges facing water systems today.

One of the primary ways utilities prevent and address water quality concerns in distribution systems is via regular hydrant flushing, yet rigorous research to evaluate the impact of full-scale flushing programs is limited. This study employed time-series and correlation analyses to evaluate the efficacy of a utility's five-month repeated conventional flushing program to reduce nitrification and improve disinfectant residual concentrations in the distribution system. Short-term water quality improvements during flushes were common across the 16 locations flushed, but lasting improvements were inconsistent as demonstrated by continued nitrification and heterogeneous water quality changes. Flushing frequencies and flow rates may need to be tailored to individual sites, even when similar water quality challenges exist. Water quality monitoring data and related analyses helped to prioritize flush sites, maximize efficiency during and between flushes, and inform decisions to implement additional interventions.

Nontuberculous mycobacteria (NTM) in drinking water are a significant public health concern. However, an incomplete understanding of the factors that influence the occurrence of NTM in drinking water limits our ability to characterize risk and prevent infection. This study sought to evaluate the influence of season and water treatment, distribution, and stagnation on NTM in drinking water. Samples were collected source-to-tap in a full-scale, chloraminated drinking water system approximately monthly from December 2019 to November 2020. NTM were characterized using culture-dependent (plate culture with matrix-assisted laser desorption ionization-time of flight mass spectrometry [MALDI-TOF MS] isolate analysis) and culture-independent methods (quantitative PCR and genome resolved metagenomics). Sampling locations included source waters, three locations within the treatment plant, and five buildings receiving water from the distribution system. Building plumbing samples consisted of first draw, five-minute flush, and full flush cold-water samples. As the study took place during the COVID-19 pandemic, the influence of reduced water usage in three of the five buildings was also investigated. The highest concentrations of NTM source-to-tap were found in the summer first draw building water samples (107gene copies/L), which also had the lowest chloramine concentrations. Flushing was found to be effective for reducing NTM and restoring disinfectant residuals, though flush times necessary to improve water quality varied by building. Clinically-relevant NTM species, includingMycobacterium avium, were recovered via plate culture, with increased occurrence observed in buildings with higher water age. Four of five NTM metagenome-assembled genomes were identified to the species level and matched identified isolates.

Cryptosporidiosis is a diarrheal disease caused by the presence of the Cryptosporidium parasite in humans and animals. The objective of this review is to provide an update on Cryptosporidium infection and describe the state of knowledge of its presence in Gabon, a country in Central Africa, through published articles on the subject and, based on the findings, to suggest priority areas for water research and monitoring. The main features of cryptosporidiosis were given with a focus on how it is transmitted and the factors that make individuals more susceptible (young and old individuals, immunocompromised individuals). Then, the methods of detection and identification of Cryptosporidium were described. As there are very few treatments for cryptosporidiosis, prevention of the disease is to be preferred in order to avoid any outbreak. Finally, the state of cryptosporidiosis to date in Gabon has been described and is followed by some consideration of possible priority research directions for prevention of risk.

Trends in microbiological drinking water quality violations in the U.S. indicate that very small and transient non-community water systems bear a disproportionate burden exacerbated by recent regulatory changes.

REFRESCH (http://energy.umich.edu/refresch) will present preliminary findings from a cross-sector workshop in Gabon exploring integrated approaches to address food, energy, and water challenges in resource constrained and development contexts. Gabon's abundant water resources, diversifying energy infrastructure, and vision for achieving national sustainability and biodiversity goals present many opportunities and challenges across sectors that may benefit from increased collaboration. A multi-day workshop at the Albert Schweitzer hospital in Lambarene is used as a vehicle for bringing together Gabonese students, educators, rural citizens, non-governmental organizations, and government representatives to share needs and ideas regarding these challenges, especially those at local and regional levels. Technical education serves as a unifying topic across workshop participants to foster a sustainable means of achieving shared visions. The workshop serves as a catalytic first step for observing and understanding ways in which such interactions and collaborations can contribute to transformational educational models that meet the needs and interests of Gabonese citizens from all backgrounds and lifestyles. It is our aim through this presentation to share a dialogue on the efficacy of development intervention approaches between the global North and South. Our presentation is aided by interactive and illustrative workshop participant profiles, video clips and photographs of workshop activities, as well sketch impressions of workshop activities from participating art and design students.

Engineering student involvement in communitybased global humanitarian development has increased in recent decades. While engineers are trained problem-solvers, it has been argued that that more traditional engineering problem solving is not sufficient for tackling the "wicked" types of problems common to community-based development projects. The ways in which problems are defined has been identified as having significant impact on design outcomes when facing wicked problems. Initial literature review demonstrated a need to examine existing empirically based global humanitarian development cases published in the literature to better understand currently practiced ways of defining problems. This study, therefore, analyzed the problem definition processes across a set of water-related global development project cases published in the literature. Qualitative data analysis utilized a problem-scoping framework from design literature as well as the main author's personal experiences in similar projects to enhance the analysis. These preliminary findings demonstrated that while student design teams are achieving considerable breadth in their problem scoping efforts, there are still important aspects of problems that do not seem to be considered. This may be contributing to under-informed solution creation in the examined projects and ultimately may be affecting design outcomes. Limitations of the study and future work are also discussed.