Drinking Water Distribution Systems Research Articles

Legionella community dynamics in a drinking water distribution system: Impact of residual chlorine depletion

This study investigated the occurrence of Legionella spp. in a chlorinated drinking water distribution system (DWDS), focusing on their community compositions and association with physicochemical water quality. Water samples were collected throughout the DWDS, covering from the treated water reservoir to distal ends. Although Legionella spp. genes were not detected at the reservoir, their abundance dramatically increased along the distribution network, reaching up to 4.4 log copies/L at distal sites. The Legionella communities were further characterized by high-throughput amplicon sequencing targeting the genus-specific 16S rRNA gene. The results revealed a diverse Legionella community, including amplicon sequence variants with high similarity (> 99 %) to potentially pathogenic species such as L. drozanskii and L. pneumophila, albeit at low levels. Moreover, Legionella community diversity increased significantly along the distribution system, leading to distinct community compositions at distal sites. Importantly, decay of residual chlorine concentration was identified as a key factor both in increasing the Legionella gene levels and shaping the community structure. Overall, this study underscores the importance of preventing pipe corrosion and maintaining adequate disinfectant residuals to minimize Legionella regrowth in DWDS.

Qualitative and Quantitative Analyses of Microplastics in Tap Water Supply Network in Iran

Background: Microplastics (MPs) exposure can affect humans in various ways, with tap water being one of the potential sources. Microplastics can absorb other pollutants and pose risks to both humans and the environment. Objectives: The aim of this study was to investigate the presence of MPs in tap water from the drinking water distribution system of Isfahan, Iran, and to determine the exposure to MPs from drinking tap water. Methods: Samples were collected from different points in the drinking water distribution system of Isfahan, Iran. Samples were prepared for analysis through filtration and chemical digestion. The MPs were counted using a scanning electron microscope (SEM), and the composition of MPs was analyzed using a micro-Raman spectrometer. Results: The concentration of MPs in tap water was found to be 287.0 ± 65.9 MPs/l. MPs ≤ 10 µm were the predominant sizes, and fibers were the predominant shape. Polyethylene terephthalate, polyethylene, and polypropylene were the most frequently identified MPs, respectively. Conclusions: Considering that the Iranian population consumes 7 - 15 liters of water daily for drinking and cooking, it is estimated that the average intake of MPs through cooking and drinking water is 2009 - 43,051 particles per day.

Effect of Pipe Materials and Interspecific Interactions on Biofilm Formation and Chlorine Resistance: Turn Enemies into Friends

Drinking water distribution systems (DWDSs) may be contaminated to various degrees when different microorganisms attach to the pipe walls. Understanding the characteristics of biofilms on pipe walls can help prevent and control microbial contamination in DWDSs. The biofilm formation, interspecific interactions, and chlorine resistance of 10 dual-species biofilms in polyethylene (PE) and cast iron (CI) pipes were investigated in this paper. The biofilm biomass (heterotrophic bacterial plate count and crystal violet) of dual species in CI pipes is significantly higher than that in PE pipes, but the biofilm activity in CI pipes is significantly lower than that in PE pipes. The interspecific interaction of Sphingomonas-containing group presented synergistic or neutral relationship in PE pipes, whereas the interspecific interaction of the Acidovorax-containing group showed a competitive relationship in CI pipes. Although interspecific relationships may help bacteria resist chlorine, the chlorine resistance was more reliant on dual-species groups and pipe materials. In CI pipes, the Microbacterium containing biofilm groups showed better chlorine resistance, whereas in PE pipes, most biofilm groups with Bacillus exhibited better chlorine resistance. The biofilm groups with more extracellular polymeric substance (EPS) secretion showed stronger chlorine resistance. The biofilm in the PE pipe is mainly protected by EPS, while both EPS and corrosion products shield the biofilms within CI pipe. These results supported that dual-species biofilms are affected by pipe materials and interspecific interactions and provided some ideas for microbial control in two typical pipe materials.

Production of biostable drinking water using a lab-scale biological trickling filter enriched with hydrogen-oxidizing bacteria

Safeguarding the drinking water quality remains a challenge from the production site to the tap. Alternatively to chemical disinfection, biostable drinking water could serve as a more sustainable approach to produce microbially safe drinking water and to maintain the microbial quality in the drinking water distribution system (DWDS). In this study, the potential of hydrogen-oxidizing bacteria (HOB) to produce biostable drinking water was examined in a continuous trickling filter supplied with hydrogen gas. A biofilm was naturally enriched for 5 months and the bacterial regrowth, invasion potential, and nutrient composition of the water were determined. Treatment improved the biostability significantly, and it is hypothesized that nutrient limitation, especially phosphorous, was a driving force. As a result, the regrowth and invasion potential were lowered, as shown with specific biostability bioassays. Overall, this study demonstrates the proof-of-concept of HOB for producing biostable drinking water through nutrient limitation.

Promoting strategies for biological stability in drinking water distribution system from the perspective of micro-nano bubbles

Microorganisms thriving in drinking water distribution system (DWDS) reduces biological stability of water, causing numerous threats to residents' drinking water safety. Traditional disinfection methods have intrinsic drawbacks, including microbial reactivation and byproduct formation, leading to waterborne diseases. Thus, effective disinfection techniques are required to ensure the microorganism's inactivation and enhance biological stability. Micro-nano bubbles (MNB) provide a promising result to these issues. This study simulates the hydraulic conditions of the tank of DWDS to investigate the enhancement of biological stability in the tank using MNBs with distinct gas sources. The analysis focused on water quality characteristics, biological stability indicators, and microbial community composition. The results showed that the dissolved gas method could generate abundant bubbles with a particle size below 1000 nm, with a concentration exceeding 106/mL in water. The particle size and Zeta potential of bubbles were crucial factors influencing in situ the ·OH generation; hence, the ·OH concentration was highly sensitive to changes in bubble size. In addition, MNBs inhibited the growth of target bacteria in water, degraded organic matter, and improved the biological stability of drinking water, reaching significant degradation rates for biodegradable dissolved organic carbon (42.74 %), assimilable organic carbon (49.49 %), and total bacteria (51.32 %). MNBs directly degraded organic matter in water by ·OH generation in situ, reducing the microbial nutrient source, thereby inhibiting microbial metabolism and activity, which induced optimum disinfection effects on Proteobacteria, Cyanobacteria, and Planctomycetota in water. In particular, the proposed experiment achieved a 100 % disinfection rate for Acinetobacter in Proteobacteria, disrupting metabolic intermediate functions with the microbial community after MNB treatment. Therefore, this study has demonstrated the potential of MNBs to enhance the biological stability of drinking water, improve water quality, and ensure residents' water health, providing valuable technical support for drinking water safety.

Study of chlorine disinfection on the formation and resuscitation of Viable but nonculturable (VBNC) bacteria in drinking water distribution systems

The presence of Viable but nonculturable (VBNC) bacteria in drinking water distribution systems(DWDS)which can recover and regain pathogenicity under certain conditions, leads to a serious underestimation of the number of microorganisms in the water and consequently microbiological risks. This study investigated E. coli's biofilm integrity and metabolic activity post‑chlorine disinfection and during resuscitation in a Circulating-flow Dynamic biofilm Contactor (CDC) reactor. Chlorine rapidly induced the VBNC state, with concentrations ≥0.3 mg/L causing all respiratory-active bacteria to transition. Higher chlorine levels damaged cell biofilms, reducing intact cell counts by 95 % and depleting ATP. VBNC bacteria in biofilms quickly regained culturability, utilizing available nutrients and ATP. Within 1–4 days, culturable bacteria in the biofilm increased from 2.29 to 4.95 log CFU/mL, significantly faster than in water. This growth corresponded with rising ATP levels, though slower than in aqueous environments. Signaling molecules (C6, C8, C12, C14) regulated gene expression during resuscitation, aiding bacterial recovery and proliferation. Chlorine disinfection disrupted intercellular communication, altering VBNC bacteria's physiological and metabolic characteristics. These findings highlight the complex dynamics of VBNC bacteria in water systems, their resuscitation potential, and the importance of biofilms in bacterial recovery, emphasizing the need for comprehensive water treatment strategies.

Enhanced inactivation of Aspergillus niger biofilms by the combination of UV-LEDs with chlorine-based disinfectants

The presence of pathogenic fungal biofilms in drinking water distribution systems poses significant challenges in maintaining the safety of drinking water. This research delved into the formation of Aspergillus niger (A. niger) biofilms and evaluated their susceptibility to inactivation using combinations of ultraviolet light emitting diodes (UV-LEDs) with chlorine-based disinfectants, including UV-LEDs/chlorine (Cl2), UV-LEDs/chlorine dioxide (ClO2), and UV-LEDs/chloramine (NH2Cl) at 265 nm, 280 nm and 265/280 nm. Results indicated that A. niger biofilms reached initial maturity within 24 h, with matured three-dimensional filamentous structures and conidiospores by 96 h. UV-LEDs combined with chlorine-based disinfectants enhanced A. niger biofilm inactivation compared to UV-LEDs alone and low-pressure UV combined with chlorine-based disinfectants. At an UV fluence of 400 mJ/cm2, log reductions of UV265, UV280, and UV265/280 combined with chlorine-based disinfectants were 2.95-fold, 3.20-fold, and 2.38-fold higher than that of UV265, UV280, and UV265/280, respectively. During the inactivation, A. niger biofilm cells experienced increased membrane permeability and intracellular reactive oxygen species levels, resulting in cellular apoptosis. Extracellular polymeric substances contributed to the higher resistance of biofilms. Regarding electrical energy consumption, the order was: UV-LEDs/ClO2 > UV-LEDs/NH2Cl > UV-LEDs/Cl2. These findings provide insights into the effective utilization of UV-LEDs for fungal biofilm disinfection.

Pipe material and natural organic matter impact drinking water biofilm microbial community, pathogen profiles and antibiotic resistome deciphered by metagenomics assembly

Biofilms in drinking water distribution systems (DWDSs) are a determinant to drinking water biosafety. Yet, how and why pipe material and natural organic matter (NOM) affect biofilm microbial community, pathogen composition and antibiotic resistome remain unclear. We characterized the biofilms’ activity, microbial community, antibiotic resistance genes (ARGs), mobile genetic elements (MGEs) and pathogenic ARG hosts in Centers for Disease Control and Prevention (CDC) reactors with different NOM dosages and pipe materials based on metagenomics assembly. Biofilms in cast iron (CI) pipes exhibited higher activity than those in polyethylene (PE) pipes. NOM addition significantly decreased biofilm activity in CI pipes but increased it in PE pipes. Pipe material exerted more profound effects on microbial community structure than NOM. Azospira was significantly enriched in CI pipes and Sphingopyxis was selected in PE pipes, while pathogen (Ralstonia pickettii) increased considerably in NOM-added reactors. Microbial community network in CI pipes showed more edges (CI 13520, PE 7841) and positive correlation proportions (CI 72.35%, PE 61.69%) than those in PE pipes. Stochastic processes drove assembly of both microbial community and antibiotic resistome in DWDS biofilms based on neutral community model. Bacitracin, fosmidomycin and multidrug ARGs were predominant in both PE and CI pipes. Both pipe materials and NOM regulated the biofilm antibiotic resistome. Plasmid was the major MGE co-existing with ARGs, facilitating ARG horizontal transfer. Pathogens (Achromobacter xylosoxidans and Ralstonia pickettii) carried multiple ARGs (qacEdelta1, OXA-22 and aadA) and MGEs (integrase, plasmid and transposase), which deserved more attention. Microbial community contributed more to ARG change than MGEs. Structure equation model (SEM) demonstrated that turbidity and ammonia affected ARGs by directly mediating Shannon diversity and MGEs. These findings might provide a technical guidance for controlling pathogens and ARGs from the point of pipe material and NOM in drinking water.

Persistent free radicals in natural organic matter activated by iron particles enhanced disinfection byproduct formation

The widespread presence of iron (Fe) particles and natural organic matter (NOM) in drinking water distribution systems (DWDS) can significantly affect tap water quality, contributing to aesthetic issues and potentially generating harmful disinfection byproducts (DBPs). This study revealed that Fe particles, when combined with humic acid (HA), substantially increased DBP formation during chlorination. Fe particles (particularly preformed Fe particles) significantly increased haloacetic acid (HAA) formation by activating the persistent free radicals (PFRs) in the HA. Compared with the control system without Fe particles, greater than 2 times of HAA increase were observed for the system with Fe pariticles. PFRs accumulated on Fe particle surface could generate hydroxyl radicals, facilitating the decomposition of HA into smaller molecules, which were more reactive with chlorine disinfectants, thus elevated the DBP formation including both known and unknown N-DBPs and Cl-DBPs. The DBP promotion effect of in-situ formed Fe particles was much less than that of preformed Fe particles although both in-situ formed and preformed Fe particles could accumulate PFRs from HA. In-situ formed particles primarily accumulated carbon-centered PFRs, while preformed particles accumulated oxygen-centered PFRs. To mitigate the Fe particle induced water quality risks, it is crucial to control iron pipe corrosion and iron release in DWDS. In addtion, the optimization of treatment processes such as coagulation and filtration to more completely remove NOM and Fe particles could help minimize the DBP formation.

Disruptive effects of sewage intrusion into drinking water: Microbial succession and organic transformation at molecular level

Drinking water distribution systems are increasingly vulnerable to sewage intrusion due to aging water infrastructure and intensifying water stress. While the health risks associated with sewage intrusion have been extensively studied, little is known about the impacts of intruded bacteria and dissolved organic matter (DOM) on microbiology in drinking water. In this dynamic study, we demonstrate that the intrusion of 1 % sewage into tap water resulted in immediate contamination, including an 8-fold increase in biomass (TCC), a 48.9 % increase in bacterial species (ASVs), a 12.5 % increase in organic carbon content (DOC), and a 13.5 % increase in unique DOM molecular formulae. Over time, sewage intrusion altered tap water microbiology by accelerating bacterial growth rates (5-fold faster), selectively promoting ASVs in community succession, and producing 998 more unique DOM formulae. More significantly, statistical analysis revealed that the intrusion of 1 % sewage shifted the driving force of bacterial and DOM composition covariance from a DOM-dependent process in tap water to a bacterial-governed process post-intrusion. Our results clearly demonstrate the disruptive effects of sewage intrusion into tap water, emphasizing the urgent need to consider the long-lasting impacts of sewage intrusion in drinking water distribution systems, in addition to its immediate health risks.

Ice slurry pigging technology in drinking water distribution system: From flow mechanisms to pipelines cleaning application

Drinking water distribution systems are prone to (bio)fouling over time, negatively impacting drinking water quality. Ice slurry pigging is a promising technology used to remove solids attached to the inner parts of the pipe walls with ice-water mixture. To understand the ice slurry pigging flow characteristics and optimize its operations, this study presents the development of a Computational Fluid Dynamics model (CFD) combined with the Kinetic Theory of Granular Flow model (KTGF) and a thermal model. Firstly, the model is validated with experimental data from the literature on solid-liquid Two-Phase Flow (TPF), including flow characteristics and thermal effects. Secondly, simulations for a typical ice slurry pigging process show uneven ice phase fraction and shear stress distributions in the main pipe flow and vertical direction. Results indicate that the main limitations of effective pipe cleaning are due to buoyancy and thermal effects. Moreover, ice slurry with 1.0 mm ice particles performs better in providing effective shear stress compared to 0.1 mm, 0.5 mm, and 1.5 mm ice particles. Additionally, the optimal injection ratios of ice slurry with 1.0 mm are determined to be over 0.3 and 0.26 when cleaning pipeline lengths within 500 m and 1000 m, respectively.

Drinking Water and Biofilm as Sources of Antimicrobial Resistance in Free-Range Organic Broiler Farms.

Drinking water distribution systems (DWDSs) represent an ideal environment for biofilm formation, which can harbor pathogenic and antimicrobial-resistant bacteria. This study aimed to assess longitudinally the microbial community composition and antimicrobial resistance (AMR), as determined by 16S rRNA NGS and qPCR, respectively, in drinking water (DW) and biofilm from DWDSs, as well as faeces, of free-range organic broiler farms. The role of DWDSs in AMR gene (ARG) dissemination within the farm environment and transmission to animals, was also assessed. DW and biofilm microbial communities differed from those of faecal samples. Moreover, potentially pathogenic and opportunistic bacteria (e.g., Staphylococcaceae) were identified in water and biofilms. High prevalence and abundance of ARGs conferring resistance to carbapenems (i.e., blaNDM), 3rd and 4th generation cephalosporins (i.e., blaCMY-2), (fluoro)quinolones (i.e., qnrS), and polymyxins (i.e., mcr-3 and mcr-5) were detected in DW, biofilm, and faecal samples, which is of concern for both animal and human health. Although other factors (e.g., feed, pests, and wildlife) may contribute to the dissemination of AMR in free-range organic poultry farms, this study indicates that DWDSs can also play a role.

Formation, speciation, and temporal variability of DBPs in drinking water distribution systems in the context of ASR operations and extended storage periods

As climate change induces changes in water quality and available water quantity of drinking water supply sources, the final product water quality changes in terms of trace organics including disinfection byproducts (DBPs) formed during water treatment. In this study, the seasonal variability and speciation of DBPs across nine sample sites within a drinking water distribution system serving ∼400k people over a one-year period was investigated considering the governing parameters of water quality and treatment/transport/storage of finished water. The system considered treats surface water from a river and practices aquifer storage and recovery to address seasons water availability changes. Eighty-eight (88) sample sets were collected and held for 6-months in the laboratory to simulate extended storage scenarios associated with ASR operations, and each was analyzed at 9 different timesteps for concentration and speciation of chlorinated DBPs. Samples from groundwater influenced sites exhibited significantly lower total organic carbon (TOC) compared to other sites from the river source, and also were observed to have the lowest DBP formation. Three sites exceeded the Maximum Contaminant Level (MCL) for four total trihalomethanes (THM4) within 30–60 days of storage. Chloroform was the predominant THM4 species, even in groundwater-influenced locations, whereas di- and tri-chloroacetic acid (DCA and TCA) were the most prevalent haloacetic acids (HAA5). Extended water age at one site, coupled with low initial chlorine concentrations exhibited higher initial THM4 concentrations and flat DBP formation curves. The study results provide new insights into DBP occurrence and fate in drinking water distribution systems which consider water storage such as in ASR.

The impact of methylparaben and chlorine on the architecture of Stenotrophomonas maltophilia biofilms

The biofilm architecture is significantly influenced by external environmental conditions. Biofilms grown on drinking water distribution systems (DWDS) are exposed to environmental contaminants, including parabens, and disinfection strategies, such as chlorine. Although changes in biofilm density and culturability from chemical exposure are widely reported, little is known about the effects of parabens and chlorine on biofilm morphology and architecture. This is the first study evaluating architectural changes in Stenotrophomonas maltophilia colony biofilms (representatives of bacterial communities presented in DWDS) induced by the exposure to methylparaben (MP) at environmental (15 μg/L) and in-use (15 mg/L) concentrations, and chlorine at 5 mg/L, using widefield epi-fluorescence mesoscopy with Mesolens. The GFP fluorescence of colony biofilms allowed the visualization of internal structures and Nile Red fluorescence permitted the inspection of the distribution of lipids. Our data show that exposure to MP triggers physiological and morphological adaptation in mature colony biofilms by increasing the complexity of internal structures, which may confer protection to embedded cells from external chemical molecules. These architectural modifications include changes in lipid distribution as an adaptive response to MP exposure. Although chlorine exposure affected colony biofilm diameter and architecture, the colony roundness was completely affected by the simultaneous presence of MP and chlorine. This work is pioneer in using Mesolens to highlight the risks of exposure to emerging environmental contaminants (MP), by affecting the architecture of biofilms formed by drinking water (DW) bacteria, even when combined with routine disinfection strategies.

Effect of antibiotics and antibiotic by-products on the chlorine resistance of biofilms in drinking water distribution systems

This study investigated the effects of tetracycline (TC) and sulfadiazine (SD), along with their degradation products, on biofilm chlorine resistance. The results showed that low concentrations of antibiotics and their degradation products promoted biofilm formation on tube surfaces and increased resistance to chlorine. There was a positive correlation between antibiotic levels, degradation products, and biofilm chlorine resistance within a specific concentration range. SD had a more significant impact on biofilm chlorine resistance compared to TC. The presence of both antibiotics and their degradation products in water led to an increase in biofilm chlorine resistance, especially when combined with 0.3 mg/L sodium hypochlorite. The study shows a positive association between antibiotic and degradation product concentrations and the biofilms' improved chlorine resistance, a phenomenon that could have major consequences for water treatment efforts. Additionally, higher concentrations of antibiotics and their degradation products were associated with reduced biodiversity within the biofilm. Overall, the findings suggest that the presence of antibiotics and their degradation products can influence biofilm formation, alter bacterial species composition, and enhance biofilm resistance to chlorine in drinking water distribution systems. This fresh perspective on the relationship between pharmaceutical residues and microbial communities in water systems could transform our approach to assuring water safety and combatting antimicrobial resistance.

Fungal presence and health implications in hospital water systems

ABSTRACT Given the increasing occurrence of invasive fungal infections and the limited efficacy of modern antifungal medications, it is crucial to disseminate information regarding the potential sources of nosocomial mycoses through the One Health approach. This study investigated the presence and antifungal susceptibility of fungi in biofilm and water samples obtained from the drinking water distribution system (DWDS) of hospitals. The positivity rate for fungi in biofilm and water samples was 41% and 9%, respectively, with Aspergillus species, a significant causative agent of nosocomial mycoses, being the predominant fungi identified. Analysis of antifungal susceptibility test revelead a comparable resistance profile between some isolated species from the DWDS and those reported for certain clinical samples. While further research is required to determine the specific contribution of waterborne fungi to nosocomial fungal infections, our results emphasize the importance of controlling biofilm formation within DWDSs, particularly in high-risk hospital wards.

Alternative for HPC22 after repairs in the drinking water distribution system

There is a risk of contamination by (pathogenic) microorganisms from the outside environment into the drinking water during maintenance or pipe breaches in the drinking water distribution system (DWDS) and, consequently, the drinking water distributed to consumers may result in possible detrimental effects on public health. Traditional time-consuming microbiological testing is, therefore, performed to confirm drinking water is not microbially contaminated. This is done by culturing methods of the faecal indicators Escherichia coli, intestinal enterococci and the technical parameters coliform bacteria and heterotrophic plate counts at 22 °C (HPC22). In this study, fast methods (adenosine triphosphate (ATP), flow cytometry, enzyme activity and qPCR) were compared as an alternative for HPC22. Using dilution series and field samples, ATP (ATPtotal-lab and ATPcell-mob) and enzymatic activity (ALP-2) methods proved to be the more reliable and sensitive than flow cytometry and qPCR methods for detecting microbiological contaminations in drinking water. Significant (p < 0.05) and relatively strong correlations (R2 = 0.61–0.76) were obtained between HPC22 and both ATP methods, enzyme activity and qPCR parameters, but relations with flow cytometry were weak (R2 = 0.24 – 0.52). The samples taken after repairs or a calamity from the DWDS showed in general limited variation in the HPC22 count and were in most cases below the guidance level of 1,000 CFU/mL. We recommend that the best performing alternative methods, i.e. ATPtotal-lab and ATPcell-mob and ALP-2, should be included next to HPC22 in additional field studies to further test and compare these methods to be able to decide which fast method can replace HPC22 analysis after maintenance work in the DWDS.

Exploring the potential of machine learning to understand the occurrence and health risks of haloacetic acids in a drinking water distribution system

Determining the occurrence of disinfection byproducts (DBPs) in drinking water distribution system (DWDS) remains challenging. Predicting DBPs using readily available water quality parameters can help to understand DBPs associated risks and capture the complex interrelationships between water quality and DBP occurrence. In this study, we collected drinking water samples from a distribution network throughout a year and measured the related water quality parameters (WQPs) and haloacetic acids (HAAs). 12 machine learning (ML) algorithms were evaluated. Random Forest (RF) achieved the best performance (i.e., R2 of 0.78 and RMSE of 7.74) for predicting HAAs concentration. Instead of using cytotoxicity or genotoxicity separately as the surrogate for evaluating toxicity associated with HAAs, we created a health risk index (HRI) that was calculated as the sum of cytotoxicity and genotoxicity of HAAs following the widely used Tic-Tox approach. Similarly, ML models were developed to predict the HRI, and RF model was found to perform the best, obtaining R2 of 0.69 and RMSE of 0.38. To further explore advanced ML approaches, we developed 3 models using uncertainty-based active learning. Our findings revealed that Categorical Boosting Regression (CAT) model developed through active learning substantially outperformed other models, achieving R2 of 0.87 and 0.82 for predicting concentration and the HRI, respectively. Feature importance analysis with the CAT model revealed that temperature, ions (e.g., chloride and nitrate), and DOC concentration in the distribution network had a significant impact on the occurrence of HAAs. Meanwhile, chloride ion, pH, ORP, and free chlorine were found as the most important features for HRI prediction. This study demonstrates that ML has the potential in the prediction of HAA occurrence and toxicity. By identifying key WQPs impacting HAA occurrence and toxicity, this research offers valuable insights for targeted DBP mitigation strategies.

Estimating the risk of gastrointestinal illness associated with drinking tap water in Norway: a prospective cohort study

BackgroundThe delivery of safe drinking water has high public health relevance, as reflected in the Sustainable Development Goals (SDG6). Several precautionary actions have reduced the burden associated with infectious diseases in high-income countries; however, pollution in source waters, inadequate disinfection, and premise plumbing, along with an increased awareness that intrusion in the drinking water distribution system, represents risk factors for gastrointestinal illness linked to consume of drinking water. Sporadic cases of waterborne infections are expected to be underreported since a sick person is less likely to seek healthcare for a self-limiting gastrointestinal infection. Hence, knowledge on the true burden of waterborne diseases is scarce. The primary aim with the present study was to estimate the risk of gastrointestinal illness associated with drinking tap water in Norway.MethodsWe conducted a 12-month prospective cohort study where participants were recruited by telephone interview after invitation based on randomised selection. A start up e-survey were followed by 12 monthly SMS questionnaires to gather information on participants characteristics and drinking tap water (number of 0.2L glasses per day), incidence, duration and symptoms associated with gastrointestinal illness. Associations between the exposure of drinking tap water and the outcome of risk of acute gastrointestinal illness (AGI) were analysed with linear mixed effects models. Age, sex, education level and size of the drinking water supply were identified as potential confounders and included in the adjusted model.ResultsIn total, 9,946 persons participated in this cohort study, accounting for 11.5% of all invited participants. According to the data per person and month (99,446 monthly submissions), AGI was reported for 5,508 person-months (5.5 per 100 person-months). Severe AGI was reported in 819 person-months (0.8 per 100 person-months). Our study estimates that 2–4% of AGI in Norway is attributable to drinking tap water.ConclusionsThis is the largest cohort study in Norway estimating the burden of self-reported gastrointestinal infections linked to the amount of tap water drunk in Norway. The data indicate that waterborne AGI is not currently a burden in Norway, but the findings need to be used with caution. The importance of continued efforts and investments in the maintenance of drinking water supplies in Norway to address the low burden of sporadic waterborne cases and to prevent future outbreaks needs to be emphasised.

Survival and Growth of Asellus aquaticus on Different Food Sources from Drinking Water Distribution Systems

Invertebrates, including Asellidae, are part of the natural ecosystem of the drinking water distribution system (DWDS) and are known to cause a nuisance to consumers. In addition, recently, the potential role of the species Asellus aquaticus (L. 1758) in the regrowth of Aeromonas bacteria was published. Aeromonas is included in the Dutch drinking water guidelines as a process parameter, and the guideline values are regularly exceeded. Although neither A. aquaticus nor Aeromonas is associated with health risks, the Evides drinking water utility shows a strong interest in the possible reasons for these exceedances and possible control measures. In surface waters, Asellidae feed mainly on decaying leaves that are abundantly present. These food sources are not present in the DWDS. Therefore, we determined suitable food sources for A. aquaticus in the DWDS. Laboratory experiments show that A. aquaticus individuals survive on biofilm on pipe wall material and loose deposits (sediments) collected from DWDS. Growth and survival rates on these loose deposits were even higher than on the positive control (decaying leaves). As the basis of these loose deposits is inorganic (iron deposits, sand, and pipe particles), the organic matter (living and decaying bacteria, protozoans, fungi, and invertebrates) must be their substrate. These experiments validate hypotheses that Asellidae can grow and survive on organic matter in deposits in DWDS.