Drinking Water Distribution Systems Research Articles

Effects of chloride on corrosion scale compositions and heavy metal release in drinking water distribution systems

Variations in water chemistry may lead to the release of harmful heavy metals in drinking water distribution systems (DWDSs). In this study, the effects of chloride on the release of heavy metals such as Fe, Mn, As, Cr, Mo, V, Sr, and Co were examined using steel and cast iron pipe loops. After chloride was added, the relative contents of goethite (α-FeOOH), lepidocrocite (γ-FeOOH), and siderite (FeCO3) in pipe scales increased, but the contents of magnetite (Fe3O4) decreased. The most prevalent compounds were α-FeOOH and γ-FeOOH. When the chloride levels were increased, the effluent concentrations of Fe, Mn, As, Cr, Mo, V, Sr, and Co significantly increased. These heavy metals were released presumably because of the destabilization and dissolution of corrosion scales induced by chloride and adsorption site competition. Strong positive correlations were also observed between Fe&Mn, Fe/Mn&As, Fe/Mn&Cr, Fe/Mn&Mo, Fe/Mn&V, Fe/Mn&Sr, and Fe/Mn&Co, indicating the co-release of Fe, Mn, and other metals. This study may be helpful for the potential strategies on avoidance of heavy metal release and improvement of water supply security.

Corrosion of pipes for conveying drinking water in Hong Kong: mechanisms and controlling strategies

A drinking water distribution system (DWDS) ensures access to safe water and provides the basis for city life. However, the pipes in DWDSs are threatened by corrosion externally and internally. This paper critically reviews the mechanisms and types of corrosion in pipes for drinking water, followed by an outline of the related controlling strategies. Special focus is accorded to pipes under the soil environment near coastal areas subjected to seawater intrusion. The corrosion that happens internally (erosion-corrosion, microbially influenced corrosion, and other ions) or those that occur externally (corrosive soils, dissimilar metals, stray current, coating damage, and microbial-influenced corrosion) eventually leads to electrolytic corrosion. It is found that soft soil (partially due to seawater intrusion) is a significant threat to corrosion in DWDSs because it is corrosive and may cause external stress problems for existing DWDSs. Some suggestions and controlling strategies are proposed in the current review.

The stress response mechanisms and resistance change of chlorine-resistant microbial community at multi-phase interface under residual antibiotics in drinking water distribution system

The presence of multiple trace amounts of antibiotics in drinking water has recently drawn much attention. However, synergistic effects between disinfectants and antibiotics often occur in pipeline due to the presence of residual disinfectants. How this interaction affects the drinking water microbial community remains unknown. Herein, reactors with 2 h of hydraulic retention time (HRT) were constructed to simulate the drinking water distribution system (DWDS), and the antibiotics were continuously discharged to the reactor. Sulfamethoxazole (SMX) was used as a representative antibiotic, and treatment protocols with and without disinfectants were compared. High-throughput sequencing and metagenome were used to study the microbial community and function in polyethylene (PE) and ductile cast iron (DI) (protected by cement mortar lining) pipes. By measuring the enzyme activity and ATP content, we found that disinfectant exposure could not only increase the secretion of biofilm EPS, but also improve the bacterial activity to a certain extent. The synergistic effect of antibiotics and disinfectants could increase the activity of oxidative stress-related enzymes in microbial communities, and the main effect was antibiotic stress. This study not only provides insights into how to inhibit the transmission process of antibiotic resistance genes (ARGs) in biofilm in DWDS, but also provides enlightenment for the harm of ARGs in all carriers where biofilms may exist in water plants.

Assessing Uncertainties in Mechanistic Modeling of Quality Fluctuations in Drinking Water Distribution Systems

Assessing Uncertainties in Mechanistic Modeling of Quality Fluctuations in Drinking Water Distribution Systems

Source to tap investigation of natural organic matter in non-disinfected drinking water distribution systems

Characteristics of natural organic matter present in drinking water from an undisinfected system fed on groundwater were investigated by spectroscopic methods highlighting changes due to seasonality, treatment and water distribution.

Study on a new index for yellow water problem during source water switch and its application on one real project

The evaluation of yellow water problem in drinking water distribution systems (DWDSs) by Larson ratio, Langlier saturation index is associated with fairly large uncertainty. As the background, one city in East China plans to change its water source from the local River A and River B into a new Lake C. Real servicing pipes were excavated in this city and assembled into 12 pipe section reactors (PSRs). The objectives of this study were to develop a more accurate index to predict the iron release in DWDSs, to verify the validity by simulation experiments with PSRs and to develop the reconditioning measures for the forthcoming source water switching project. A new index called iron stability index (ISI) was proposed by dividing alkalinity with the Larson ratio. Its validity was verified by the data in this study and literatures. ISI present closer linear relationship than that of LR and LSI in the situation where the concentration of anions (chloride and sulfate), and alkalinity in raw water and the switched water change more drastically. The water source switching from the local River A to the new Lake C was predicted not able to bring yellow water problem while that for the local River B to the Lake C has the risk. The water quality reconditioning measures were evaluated to address that concern and applied successfully in this project.

Effects of disinfectant type and dosage on biofilm's activity, viability, microbiome and antibiotic resistome in bench-scale drinking water distribution systems

Drinking water distribution systems (DWDSs) are important for supplying high-quality water to consumers and disinfectant is widely used to control microbial regrowth in DWDSs. However, the disinfectant's influences on microbial community and antibiotic resistome in DWDS biofilms and the underlying mechanisms driving their dynamics remain elusive. The study investigated the effects of chlorine and chloramine disinfection on the microbiome and antibiotic resistome of biofilms in bench-scale DWDSs using metagenomics assembly. Additionally, the biofilm activity and viability were monitored based on adenosine triphosphate (ATP) and flow cytometer (FCM) staining. The results showed that both chlorine and chloramine disinfectants decreased biofilm ATP, although chloramine at a lower dosage (1 mg/L) could increase it. Chloramine caused a greater decrease in living cells than chlorine. Furthermore, the disinfectants significantly lowered the microbial community diversity and altered microbial community structure. Certain bacterial taxa were enriched, such as Mycobacterium, Sphingomonas, Sphingopyxis, Azospira, and Dechloromonas. Pseudomonas aeruginosa exhibited high resistance towards disinfectants. The disinfectants also decreased the complexity of microbial community networks. Some functional taxa (e.g., Nitrospira, Nitrobacter, Nitrosomonas) were identified as keystones in chloramine-treated DWDS microbial ecological networks. Stochasticity drove biofilm microbial community assembly, and disinfectants increased the contributions of stochastic processes. Chlorine had greater promotion effects on antibiotic resistance genes (ARGs), mobile genetic elements (MGEs) and ARG hosts than chloramine. The disinfectants also selected pathogens, such as Acinetobacter baumannii and Klebsiella pneumonia, and these pathogens also harbored ARGs and MGEs. Overall, this study provides new insights into the effects of disinfectants on biofilm microbiome and antibiotic resistome, highlighting the importance of monitoring and managing disinfection practices in DWDSs.

Integrated EPANET-MSX process models of chlorine and its by-products in drinking water distribution systems.

EPANET and its commercial derivatives are the most widely-used software packages for modeling free chlorine and its by-products in drinking water distribution systems. Yet, they are not sufficiently accurate, general, or efficient for deriving optimal chlorine dosing strategies at different seasonal temperatures. To overcome EPANET's limitations, an integrated set of rigorously validated multispecies process models are proposed for application within the EPANET-MSX environment. An executable (command-line) version of these MSX models is supplied for use either within the MSX environment or embedded in commercial versions of MSX. A new general method was devised to obtain output of any intermediate coefficient or variable involved in the simulation. This overcomes MSX's limited output options. When the debugged models were applied to a real distribution system, the optimal chlorine dose for summer required almost double the chlorine dose needed in winter. A lower initial dose combined with a downstream booster dose required less chlorine in total. Formal optimization techniques are needed to efficiently obtain similar strategies in more complex systems. PRACTITIONER POINTS: EPANET water quality models are not accurate or general enough for deriving optimal chlorine dosing strategies in distribution systems. Integrated EPNET-MSX models of chlorine reactions in bulk water and at pipe walls, and associated by-product formation, overcome EPANET's limitations. To verify model authenticity, a general technique was developed to obtain values of coefficients and variables within an EPANET-MSX simulation. EPANET-MSX command lines implementing these integrated EPANET-MSX models are presented with verified results for optimal initial and booster dosing strategies. Optimal summer dosing in a real system of rough pipes was almost double that required in winter.

Modeling Nicotine-Induced Chlorine Loss in Drinking Water Using Updated EPANET-MSX.

Multispecies water quality modeling is critical for simulating complex chemical reactions in drinking water distribution systems. An updated EPANET 2.2-compatible version of EPANET multi-species eXtension (EPANET-MSX) was used, which included dispersion and improved mass balance reporting, to simulate an experimental study. The use of EPANET-MSX was supplemented by an automated Python script to process experimental data, handle model execution, and analyze results. Nicotine-associated chlorine loss in drinking water-initially investigated from a drinking water security perspective-modeled with EPANET-MSX was compared with bottle test and test injection data. Two reaction models were tested (with and without a reactive intermediate), and the model that included a reactive intermediate nicotine species using dispersion was found to produce the best model agreement with experimental data. These results provide a demonstration of the new features within EPANETMSX in the context of the nicotine-chlorine reaction.

Changes of putative pathogenic species within the water bacterial community in large-scale drinking water treatment and distribution systems

Although the management of microbes in drinking water is of paramount importance for public health, there remain challenges in comprehensively examining pathogenic bacteria in the water supply system at the species level. In this study, high-throughput sequencing of nearly full-length 16S rRNA genes was performed to investigate the changes of the water bacterial community in three large-scale drinking water treatment plants (DWTPs) and their corresponding distribution systems during winter and summer. Our findings revealed significant differences in the bacterial community structure between winter and summer water samples for each DWTP and its distribution management area (DMA). In the groundwater-fed DWTP, selective enrichment of mycobacterial species was observed in both seasons, and the subsequent DMA also exhibited strong selection for specific mycobacterial species. In one of the surface water-fed DWTPs, certain Legionella species present in the source water in winter were selectively enriched in the bacterial community after pre-oxidation, although they were susceptible to the subsequent purification steps. A variety of putative pathogenic species (n = 83) were identified based on our pathogen identification pipeline, with the dominant species representing opportunistic pathogens commonly found in water supply systems. While pathogen removal primarily occurred during the purification processes of DWTPs, especially for surface water-fed plants, the relative abundance of pathogenic bacteria in the DMA water flora was lower than that in the DWTP effluent flora, indicating a diminished competitiveness of pathogens within the DMA ecosystem.

Algorithms to mimic human interpretation of turbidity events from drinking water distribution systems

Abstract Deriving insight from the increasing volume of water quality time series data from drinking water distribution systems is complex and is usually situation- and individual-specific. This research used crowd-sourcing exercises involving groups of domain experts to identify features of interest within turbidity time series data from operational systems. The resulting labels provide insight and a novel benchmark against which algorithmic approaches to mimic the human interpretation could be evaluated. Reflection of the results of the labelling exercises resulted in the proposal of a turbidity event scale consisting of advisory <2 NTU, alert 2 < NTU < 4, and alarm >4 NTU levels to inform utility response. Automation, for scale up, was designed to enable event detection within these categories, with the <2NTU category being the most challenging. A time-based averaging approach, based on data at the same time of day, was found to be most effective for identifying these advisory events. The automation of event detection and categorisation presented here provides the opportunity to gain actionable insight to safeguard drinking water quality from ageing infrastructure.

Harvested versus conditioned new test pieces in drinking water lead or copper corrosion testing

Abstract Corrosion monitoring apparatuses are important tools in drinking water distribution systems for empirically assessing effectiveness of corrosion treatment before application to the entire water system. They are also important for tracking lead or copper release in the distribution system before, during, and after a treatment strategy is in place. A major debate is whether to use test pieces of pipe harvested from the distribution system or to use conditioned new metal surfaces. Harvested and conditioned new test pieces were studied in multiple types of water systems using analysis of chemical scales, biofilms, and metals release data. It was found that both methods of testing are equally valid if procedures follow certain conditions: (1) apparatus configuration and operation are consistent, (2) properties of distribution system pipe wall accumulations are known, (3) dissolved and particulate metal fractions are determined, and (4) apparatus metal release data are correlated with residential data. The use of conditioned new test pieces, obtainable with relative ease, lowers corrosion control study costs, providing a tool for water systems of all sizes to select the most effective corrosion control strategy and to pro-actively track lead and copper release trends in the distribution system.

Modeling Chlorine Decay in Reclaimed Water Distribution Systems—A Lisbon Area Case Study

Climate change has emerged as a global challenge, with consequences for the environment and societies. To mitigate its impacts, reclaimed water (RW) offers potential by reducing water withdrawal and minimizing pollution discharges in the environment. Safe RW requires disinfection and a sound management of chlorine residuals throughout the RW distribution systems (RWDSs). This study focuses on implementing and calibrating a chlorine decay model using EPANET-MSX in a real RWDS, incorporating both bulk and wall decays. The bulk decay accounts for reactions of monochloramine formation, auto-decomposition, and depletion by a parallel second-order mechanism where monochloramine reacts both with fast and slow organic matter reactive fractions. Two wall decays were considered in the RWDS, one in the tank, modeled through an overall wall decay constant, and one in the pipes, modeled through a wall decay constant. Field experiments were conducted to calibrate the complete model. This model was used as a support tool to diagnose the RWDS status condition and cleaning needs, and to manage its operation. Through simulated scenarios considering monochloramine wall decays similar to those observed in drinking water distribution systems, the model allowed predicting adequate chlorine dosing in summer and winter scenarios, so as to guarantee monochloramine concentrations between 1 mg/L and 5 mg/L through the network. These results point to the potential use of much lower doses than the ones currently applied.

Assessing the Impacts of Lead Corrosion Control on the Microbial Ecology and Abundance of Drinking-Water-Associated Pathogens in a Full-Scale Drinking Water Distribution System.

Increases in phosphate availability in drinking water distribution systems (DWDSs) from the use of phosphate-based corrosion control strategies may result in nutrient and microbial community composition shifts in the DWDS. This study assessed the year-long impacts of full-scale DWDS orthophosphate addition on both the microbial ecology and density of drinking-water-associated pathogens that infect the immunocompromised (DWPIs). Using 16S rRNA gene amplicon sequencing and droplet digital PCR, drinking water microbial community composition and DWPI density were examined. Microbial community composition analysis suggested significant compositional changes after the orthophosphate addition. Significant increases in total bacterial density were observed after orthophosphate addition, likely driven by a 2 log 10 increase in nontuberculous mycobacteria (NTM). Linear effect models confirmed the importance of phosphate addition with phosphorus concentration explaining 17% and 12% of the variance in NTM and L. pneumophila density, respectively. To elucidate the impact of phosphate on NTM aggregation, a comparison of planktonic and aggregate fractions of NTM cultures grown at varying phosphate concentrations was conducted. Aggregation assay results suggested that higher phosphate concentrations cause more disaggregation, and the interaction between phosphate and NTM is species specific. This work reveals new insight into the consequences of orthophosphate application on the DWDS microbiome and highlights the importance of proactively monitoring the DWDS for DWPIs.

Spatiotemporal trends in particle-associated microbial communities in a chlorinated drinking water distribution system

Various spatiotemporal, hydraulic, and water quality parameters can affect the microbial community composition of water within drinking water distribution systems (DWDSs). Although some relationships between various paravmeters and microbial growth are known, the effects of spatial and temporal trends on particle-associated microbial communities in chlorinated DWDSs remain poorly understood. The objectives of this study were to characterize the microbial community composition of both particle-associated bacteria (PAB) and total bacteria (TB) within a full-scale chlorinated DWDS, and assess relationships between microbiavvl community and various spatiotemporal, hydraulic, and water quality parameters. Bulk water samples were collected from the treatment plant, a storage tank, and 12 other sites in a rural chlorinated DWDS at varying distances from the treatment plant on four sampling dates spanning six months. Amplicon sequencing targeting the 16S rRNA gene was performed to characterize the microbial community. Gammaproteobacteria dominated the DWDS, and hydraulic parameters were well-correlated with differences in microbial communities between sites. Results indicate that hydraulic changes may have led to the detachment of biofilms and loose deposits, subsequently affecting the microbial community composition at each site. Spatial variations in microbial community were stronger than temporal variations, differing from similar studies and indicating that the highly varied hydraulic conditions within this system may intensify spatial variations. Genera containing pathogenic species were detected, with Legionella and Pseudomonas detected at every site at least once and Mycobacterium detected at most sites. However, only one sample had quantifiable Pseudomonas aeruginosa through quantitative polymerase chain reaction (qPCR), and no samples had quantifiable Legionella pneumophila or Mycobacterium avium, indicating a low human health risk. This study establishes spatial variations in PAB associated with varied hydraulic conditions as an important factor driving microbial community within a chlorinated DWDS.

Composition of active bacterial communities and presence of opportunistic pathogens in disinfected and non-disinfected drinking water distribution systems in Finland

Many factors, including microbiome structure and activity in the drinking water distribution system (DWDS), affect the colonization potential of opportunistic pathogens. The present study aims to describe the dynamics of active bacterial communities in DWDS and identify the factors that shape the community structures and activity in the selected DWDSs. Large-volume drinking water and hot water, biofilm, and water meter deposit samples were collected from five DWDSs. Total nucleic acids were extracted, and RNA was further purified and transcribed into its cDNA from a total of 181 water and biofilm samples originating from the DWDS of two surface water supplies (disinfected with UV and chlorine), two artificially recharged groundwater supplies (non-disinfected), and a groundwater supply (disinfected with UV and chlorine). In chlorinated DWDSs, concentrations of <0.02–0.97 mg/l free chlorine were measured. Bacterial communities in the RNA and DNA fractions were analysed using Illumina MiSeq sequencing with primer pair 341F-785R targeted to the 16S rRNA gene. The sequence libraries were analysed using QIIME pipeline, Program R, and MicrobiomeAnalyst. Not all bacterial cells were active based on their 16S rRNA content, and species richness was lower in the RNA fraction (Chao1 mean value 490) than in the DNA fraction (710). Species richness was higher in the two DWDSs distributing non-disinfected artificial groundwater (Chao1 mean values of 990 and 1 000) as compared to the two disinfected DWDSs using surface water (Chao1 mean values 190 and 460) and disinfected DWDS using ground water as source water (170). The difference in community structures between non-disinfected and disinfected water was clear in the beta-diversity analysis. Distance from the waterworks also affected the beta diversity of community structures, especially in disinfected distribution systems. The two most abundant bacteria in the active part of the community (RNA) and total bacterial community (DNA) belonged to the classes Alphaproteobacteria (RNA 28 %, DNA 44 %) and Gammaproteobacteria (RNA 32 %, DNA 30 %). The third most abundant and active bacteria class was Vampirovibrionia (RNA 15 %), whereas in the total community it was Paceibacteria (DNA 11 %). Class Nitrospiria was more abundant and active in both cold and hot water in DWDS that used chloramine disinfection compared to non-chlorinated or chlorine-using DWDSs. Thirty-eight operational taxonomic units (OTU) of Legionella, 30 of Mycobacterium, and 10 of Pseudomonas were detected among the sequences. The (RT)-qPCR confirmed the presence of opportunistic pathogens in the DWDSs studied as Legionella spp. was detected in 85 % (mean value 4.5 × 104 gene copies/100 ml), Mycobacterium spp. in 95 % (mean value 8.3 × 106 gene copies/100 ml), and Pseudomonas spp. in 78 % (mean value 1.6 × 105 gene copies/100 ml) of the water and biofilm samples. Sampling point inside the system (distance from the waterworks and cold/hot system) affected the active bacterial community composition. Chloramine as a chlorination method resulted in a recognizable community composition, with high abundance of bacteria that benefit from the excess presence of nitrogen. The results presented here confirm that each DWDS is unique and that opportunistic pathogens are present even in conditions when water quality is considered excellent.

Application of Ice Pigging in a Drinking Water Distribution System: Impacts on Pipes and Bulk Water Quality

Ice pigging is an emerging technique for pipe cleaning in drinking water distribution systems. However, substantial confusion and controversy exist on the potential impacts of ice pigging on bulk water quality. This study monitored the microstructural features and composition of sediments and microbial community structures in bulk water in eight multimaterial Chinese networks. Chloride concentration analysis demonstrated that separate cleaning of pipes with different materials in complex networks could mitigate the risk of losing ice pigs and degrading water quality. The microstructural and trace element characterization results showed that ice pigs would scarcely disturb the inner surfaces of long-used pipes. The bacterial richness and diversity of bulk water decreased significantly after ice pigging. Furthermore, correlations were established between pipe service age, temperature, and chloride and total iron concentrations, and the 15 most abundant taxa in bulk water, which could be used to guide practical ice pigging operations.

Effect of booster disinfection on the prevalence of microbial antibiotic resistance and bacterial community in a simulated drinking water distribution system

Booster disinfection was often applied to control the microorganism's growth in long-distance water supply systems. The effect of booster disinfection on the changing patterns of antibiotic resistance and bacterial community was investigated by a simulated water distribution system (SWDS). The results showed that the antibiotic resistance bacteria (ARB) and antibiotic resistance genes (ARGs) were initially removed after dosing disinfectants (chlorine and chloramine), but then increased with the increasing water age. However, the relative abundance of ARGs significantly increased after booster disinfection both in buck water and biofilm, then decreased along the pipeline. The pipe materials and disinfectant type also affected the antibiotic resistance. Chlorine was more efficient in controlling microbes and ARGs than chloramine. Compared with UPVC and PE pipes, SS pipes had the lowest total bacteria, ARB concentration, and ARB percentage, mainly due to higher disinfectant residuals and a smoother surface. The significant correlation (rs = 0.77, p < 0.001) of the 16S rRNA genes was observed between buck water and biofilm, while the correlations of targeted ARGs were found to be weak. Bray-Curtis similarity index indicated that booster disinfection significantly changed the biofilm bacterial community and the disinfectant type also had a marked impact on the bacterial community. At the genus level, the relative abundance of Pseudomonas, Sphingomonas, and Methylobacterium significantly increased after booster disinfection. Mycobacterium increased after chloramination while decreased after chlorination, indicating Mycobacterium might resist chloramine. Pseudomonas, Methylobacterium, and Phreatobacter were found to correlate well with the relative abundance of ARGs. These results highlighted antibiotic resistance shift and bacterial community alteration after booster disinfection, which may be helpful in controlling potential microbial risk in drinking water.

Synergistic effects of trace sulfadiazine and corrosion scales on disinfection by-product formation in bulk water of cast iron pipe

The effects of trace sulfadiazine (SDZ) and cast-iron corrosion scales on the disinfection by-product (DBP) formation in drinking water distribution systems (DWDSs) were investigated. The results show that under the synergistic effect of trace SDZ (10 μg/L) and magnetite (Fe3O4), higher DBP concentration occurred in the bulk water with the transmission and distribution of the drinking water. Microbial metabolism-related substances, one of the important DBP precursors, increased under the SDZ/Fe3O4 condition. It was found that Fe3O4 induced a faster microbial extracellular electron transport (EET) pathway, resulting in a higher microbial regrowth activity. On the other hand, the rate of chlorine consumption was quite high, and the enhanced microbial EET based on Fe3O4 eliminated the need for microorganisms to secrete excessive extracellular polymeric substances (EPS). More importantly, EPS could be continuously secreted due to the higher microbial activity. Finally, high reactivity between EPS and chlorine disinfectant resulted in the continuous formation of DBPs, higher chlorine consumption, and lower EPS content. Therefore, more attention should be paid to the trace antibiotics polluted water sources and cast-iron corrosion scale composition in the future. This study reveals the synergistic effects of trace antibiotics and corrosion scales on the DBP formation in DWDSs, which has important theoretical significance for the DBP control of tap water.

Microplastics and chemical leachates from plastic pipes are associated with increased virulence and antimicrobial resistance potential of drinking water microbial communities

There is increasing recognition of the potential impacts of microplastics (MPs) on human health. As drinking water is the most direct route of human exposure to MPs, there is an urgent need to elucidate MPs source and fate in drinking water distribution system (DWDS). Here, we showed polypropylene random plastic pipes exposed to different water quality (chlorination and heating) and environmental (freeze-thaw) conditions accelerated MPs generation and chemical leaching. MPs showed various morphology and aggregation states, and chemical leaches exhibited distinct profiles due to different physicochemical treatments. Based on the physiological toxicity of leachates, oxidative stress level was negatively correlated with disinfection by-products in the leachates. Microbial network analysis demonstrated exposure to leachates (under three treatments) undermined microbial community stability and increased the relative abundance and dominance of pathogenic bacteria. Leachate physical and chemical properties (i.e., MPs abundance, hydrodynamic diameter, zeta potential, total organic carbon, dissolved ECs) exerted significant (p < 0.05) effects on the functional genes related to virulence, antibiotic resistance and metabolic pathways. Notably, chlorination significantly increased correlations among pathogenic bacteria, virulence genes, and antibiotic resistance genes. Overall, this study advances the understanding of direct and indirect risks of these MPs released from plastic pipes in the DWDS.