Tap water microbiome shifts in secondary water supply for high-rise buildings.

In high-rise buildings, secondary water supply systems (SWSSs) are pivotal yet provide a conducive milieu for microbial proliferation due to intermittent flow, low disinfectant residual, and high specific pipe-surface area, raising concerns about tap water quality deterioration. Despite their ubiquity, a comprehensive understanding of bacterial community dynamics within SWSSs remains elusive. Here we show how intrinsic SWSS variables critically shape the tap water microbiome at distal ends. In an office setting, distinct from residential complexes, the diversity in piping materials instigates a noticeable bacterial community shift, exemplified by a transition from α-Proteobacteria to γ-Proteobacteria dominance, alongside an upsurge in bacterial diversity and microbial propagation potential. Extended water retention within SWSSs invariably escalates microbial regrowth propensities and modulates bacterial consortia, yet secondary disinfection emerges as a robust strategy for preserving water quality integrity. Additionally, the regularity of water usage modulates proximal flow dynamics, thereby influencing tap water's microbial landscape. Insights garnered from this investigation lay the groundwork for devising effective interventions aimed at safeguarding microbiological standards at the consumer's endpoint.

Achieving zero fouling in the ultrafiltration for secondary water supply systems in the absence of residual chlorine.

Ultrafiltration (UF) technology is widely used in secondary water supply systems (SWSS) to provide high-quality drinking water. However, the challenge of severe membrane fouling, which leads to frequent cleaning requirements, makes UF maintenance intensive. In this study, we tried to validate the feasibility of achieving zero fouling without the need for cleaning in the UF for SWSS, i.e., the fouling resistance can be maintained for a very long time without any increase. We operated dead-end UF systems at different fluxes, both with and without residual chlorine, and monitored the formation of fouling layers during filtration. The results demonstrated the successful achievement of zero fouling under a flux of 10 L/(m2 h) in the absence of chlorine, evidenced by no increase in transmembrane pressure for three months. This zero-fouling phenomenon was attributed to the formation of a self-regulating biofouling layer. This biofouling layer could degrade the deposited foulants and featured a loose morphology, facilitated by microbial activities in the cake layer. Although residual chlorine reduced the fouling rate by half at a flux of 30 L/(m2 h), it hindered the achievement of zero fouling at the lower flux of 10 L/(m2 h), due to its inhibitory effect on microbial activity. Intermittent operation of UF was effective in achieving zero fouling at higher fluxes (e.g., 30 L/(m2 h)). This benefit was primarily ascribed to the biodegradation of accumulated foulants and the expansion of biofouling layer during the pause of the intermittent filtration, which prompted the formation of biofouling layers with loose structure and balanced composition. To the best of our knowledge, this study is the first attempt to achieve zero fouling in UF for SWSS, and the findings may offer valuable insights for the development of cleaning-free and low-maintenance membrane processes.

Hidden risks: Simulated leakage of domestic sewage to secondary water supply systems poses serious microbiological risks.

There are continuous reports about the pollution of the secondary water supply systems (SWSSs), among which domestic sewage leakage is the most serious. In this study, a pilot experiment lasting 70 days was conducted to explore the changes in physicochemical water quality and the microbial profiles in SWSSs polluted by different doses of domestic sewage through qPCR and high-throughput sequencing methods. The results showed that when domestic sewage entered the simulated water storage tank, a large amount of organic matter brought by domestic sewage quickly consumed chlorine disinfectants. High pollution levels (pollution index ≥ 1/1000) were accompanied by significant increases in turbidity and ammonia nitrogen concentration (p < 0.05) and by abnormal changes in sensory properties. Although different microbial community structures were found only at high pollution levels, qPCR results showed that the abundance of the bacterial 16S rRNA gene and some pathogenic gene markers in the polluted tank increased with the pollution level, and the specific gene marker of pathogens could be detected even at imperceptible pollution levels. In particular, the high detection frequency and abundance of Escherichia coli and Enterococcus faecails in polluted tank water samples demonstrated that they can be used for early warning. Moreover, it seems that the microorganisms that came with the domestic sewage lost their cultivability soon after entering SWSSs but could recover their activities during stagnation. In addition, the biofilm biomass in the polluted tank with high pollution levels increased faster at the initial stage, while after a longer contact time, it tended to remain at the same level as the control tank. This study emphasized the high microbial risk introduced by sewage water leakage even at imperceptible levels and could provide scientific suggestions for early warning and prevention of pollution to SWSSs.

Unraveling bacterial and eukaryotic communities in secondary water supply systems: Dynamics, assembly, and health implications.

Secondary water supply systems (SWSSs) are crucial water supply infrastructures for high-rise buildings in metropolitan cities. In recent years, they have garnered public attention due to increased microbial risks. However, our understanding of SWSS microbial ecology, particularly concerning the composition of eukaryotes and the underlying mechanisms driving microbial dynamics and assembly in SWSSs, remains elusive. Herein, we conducted a comprehensive investigation on both eukaryotes and bacteria along the water transportation pathway and across various microbial habitats (water, biofilm, and sediment) in SWSSs. Sequencing results revealed that eukaryotes within SWSSs predominantly consist of protists (average abundance: 31.23%) and metazoans (20.91%), while amoebae accounted for 4.71% of the total. During water transportation from the distribution mains to taps, both bacterial and eukaryotic communities exhibited significant community shifts, and higher degrees of variation were observed for eukaryotic community among different locations within SWSSs. The normalized stochasticity ratio (NST) analysis demonstrated that bacterial community assembly was governed by stochastic processes, while eukaryotic community assembly was primarily shaped by deterministic processes. Within SWSS tanks, bacterial communities significantly varied across water, biofilm, and sediment, whereas eukaryotic communities showed minor differences among these habitats. The co-occurrence networks analysis revealed that tank biofilm and sediment harbored more eukaryote-bacterium linkages than water, suggesting biofilm and sediment might be hotspots for inter-kingdom interactions. We also applied FEAST analysis to track the source of tap water microbiota, results of which showed that household-tap bacteria mainly originated from tank water. In contrast, tank biofilm was identified as the primary microbial source to eukaryotes in household tap water. Additionally, engineering factors such as tank materials significantly affected amoeba community, and the SWSS configuration was found to influence Legionella and Mycobacterium abundances in SWSSs. Overall, results of our study shed light on the microbial ecology in SWSS and provide insights into SWSS management and health risk control.

To close or open the tank input water valve: Secondary water-supply systems with double tanks will induce a higher microbial risk.

Secondary water supply systems (SWSSs) are widely used to supply water to high-rise households in urban residential buildings. A special mode of double tanks with one used while another was spared was noted in SWSSs, which would facilitate microbial growth due to longer water stagnation in the spare tank. There are limited studies on the microbial risk of water samples in such SWSSs. In this study, the input water valves of the operational SWSSs consisting of double tanks were artificially closed and opened on time. Propidium monoazide-qPCR and high-throughput sequencing were performed to systematically investigate the microbial risks in water samples. After closing the tank input water valve, it may take several weeks to replace the bulk water in the spare tank. The residual chlorine concentration in the spare tank decreased by up to 85 % within 2-3 days compared with that in the input water. The microbial communities in the spare and used tank water samples clustered separately. High bacterial 16S rRNA gene abundance and pathogens-like sequences were detected in the spare tanks. Most antibiotic-resistant genes (11/15) in the spare tanks showed an increase in their relative abundance. Moreover, when both tanks within one SWSS were in use, the water quality of the used tank water samples deteriorated to varying degrees. Overall, running SWSSs with double tanks will reduce the replacement rate of water in one storage tank, and consumers who use taps served by the presented SWSSs may have a higher microbial risk.

A survey on heavy metal concentrations in residential neighborhoods: The influence of secondary water supply systems.

Water quality deterioration often occurs in secondary water supply systems (SWSSs), and increased heavy metal concentrations can be a serious problem. In this survey, twelve residential neighborhoods were selected to investigate the influence of SWSSs on the seasonal changes in heavy metal concentrations from input water to tank and tap water. The concentrations of nine evaluated heavy metals in all groups of water samples were found to be far below the specified standard levels in China. The concentrations of Fe, Mn, and Zn increased significantly from the input water samples to the tank and tap water samples in spring and summer (p < 0.05), especially for the water samples that had been stagnant for a long time. Negative correlations were found between most of the heavy metals and residual chlorine (Fe, Cu, Zn, and As, r = -0.186 to -0.519, p < 0.05). In particular, a high negative correlation was observed between Fe and residual chlorine (r = -0.489 to -0.519, p < 0.01) in spring and summer. Fe and Mn displayed positive correlations with turbidity (r = 0.672 and 0.328, respectively; p < 0.05). In addition, Cr and As were found to be positively associated with some nutrients (NO3-, TN, and SO42-; r = 0.420-0.786, p < 0.01). The material of the storage tanks had little influence on the difference in heavy metal concentrations. Overall, this survey illustrated that SWSSs may pose a chronic threat to water quality and could provide useful information for practitioners.

Control of maximum water age based on total chlorine decay in secondary water supply system.

97% of residential buildings are installed with secondary water supply system (SWSS) in China. In order to meet the water pressure demand, the SWSS has become a key solution to store and transport drinking water. The water age of the SWSS directly determines the quality of tap water, while total chlorine is a key indicator to evaluate the quality and safety of the water supply network. This study revealed the relationship between total chlorine and water age controlled by adjusting the liquid level of the secondary water supply tank. Models governing water age and the total chlorine concentration were developed based on the variation of the liquid level and the attenuation rate of the total chlorine in the SWSS. Furthermore, the validation was performed through case studies. The developed models can gain effective insights for determining the longest water age while guaranteeing the concentration of total chlorine meets the demand of the lower standard in SWSS. The secondary chlorine dosage would be quantified and added to the pipe network. The integration of the SWSS would be guided by water age in some old communities. The taste of tap water for direct drinking water could be improved by adjusting of water age using this model. The optimization method is easy to use for identifying efficient solutions for SWSS operation.

Monitoring and analysis of secondary water supply quality of passenger train in a certain district / 公共卫生与预防医学

Objectives To investigate the sanitary condition of the secondary water supply for passenger trains in the administration area, to evaluate the influencing factors of the secondary water supply system for passenger trains, and to put forward suggestions for improving the water quality of the secondary water supply for passenger trains. Methods The water quality of secondary water supply of 48 trains of 24 pairs of CRH type passenger trains and 160 trains of 10 pairs of type 22 passenger trains and 30 pairs of type 25 passenger trains in Lanzhou Railway Bureau in 2019 was analyzed and compared. Results The qualification rate of 208 samples tested was 73.08%. The qualification rate of secondary water supply quality of type 22 and 25 passenger trains was 62.50% and 66.67%, respectively, and the difference was not statistically significant（χ2=0.23 ，P＞0.05）. The qualification rate of secondary water supply of CRH passenger train was 97.92%, which was statistically significantly different compared with that of type 22 and 25 passenger trains（χ2=18.40, 18.15, P2=0.056, 0.054, 0.056, 0.22, 0, and 0.22, P>0.05). The total number of bacterial colonies, total coliform, turbidity and iron in the secondary water supply of type 22 and 25 passenger trains did not meet the standard, while only one water sample for the secondary water supply of CRH passenger trains did not meet the standard. Conclusion The quality of secondary water supply of CRH passenger train is obviously better than that of type 22 and 25 passenger trains. Changing the position of defecation port and water injection pipe of type 22 and 25 passenger trains, selecting non direct train defecation collection system, or adding appropriate amount of chlorine disinfectant into the water supply hose can significantly improve the qualification rate of bacteriological indexes of secondary water supply of passenger trains.

A comprehensive investigation of the microbial risk of secondary water supply systems in residential neighborhoods in a large city.

Secondary water supply systems (SWSSs) are characterized by long water stagnation and low levels of chlorine residuals, which may pose a high microbial risk to terminal users. In this study, the SWSSs of 12 residential neighborhoods in a metropolitan area of 5 million people in southeastern China were seasonally investigated to assess their microbial risks by determining more than 30 physicochemical and biological parameters. Although the microbiological quality of SWSS water met the requirements of the standards for drinking water quality of China, it did deteriorate in various aspects. The heterotrophic plate counts with R2A media were high (> 100 CFU/mL) in some SWSS tank and tap water samples. Propidium monoazide (PMA)-qPCR revealed a one magnitude higher abundance of viable bacteria in the tank and tap water samples (average 103.63±1.10 and 103.65±1.25 gene copies/mL, respectively) compared with the input water samples, and Enterococcus, Acanthamoeba, and Hartmannella vermiformis were only detected in the tanks. In particular, the high detection frequency of Legionella in 35% tank and 21% tap water samples suggested it is a supplementary microbial safety indicator in SWSSs. The microbial regrowth potential was more obvious in summer, and Illumina sequencing also demonstrated distinct seasonal changes in the relative abundance of bacterial gene sequences at the genus level. Turbidity and residual chlorine were closely connected with total bacterial biomass, and the latter seemed responsible for microbial community structure alteration. The extremely low chlorine residuals associated with a high abundance of total bacteria (as high as 106.48 gene copies/mL) and Legionella (as high as 106.71 gene copies/100 mL) in the closed valve tanks highlighted the high microbial risk increased by mishandling the operation of SWSSs. This study found that SWSSs possessed a higher microbial risk than the drinking water network, which suggested that the frequency and scope of monitoring the microbial risk of SWSSs in megacities should be strengthened for the purpose of waterborne epidemic disease prevention and control.

Response of bacterial regrowth, abundant and rare bacteria and potential pathogens to secondary chlorination in secondary water supply system.

This study investigated the effects of secondary chlorination on bacterial regrowth, microbial communities (abundant and rare taxa) and bacterial functions of pipe wall biofilm and bulk water in simulated secondary water supply system (SWSS). Continuous secondary chlorination was more effective than short-term secondary chlorination to control the bacterial regrowth in both biofilm and water samples. Bacterial diversity slightly reduced after continuous secondary chlorination, and 19.27% of the total operational taxonomic units (OTUs) were shared by biofilm and water samples, with Bacillus as the dominant genus. Abundant and rare taxa exhibited different community structures. Proteobacteria and candidate division WPS-1 predominated in abundant and rare phyla were sensitive to chlorine, while Firmicutes, Acidobacteria and Bacteroidetes, exhibited relative strong chlorine resistance. The abundant genera in control sample (e.g., Bosea, Sphingobium and Gemmata) exhibited poor tolerance to chlorine, while Bacillus in biofilm and Defluviimonas in water were the main chlorine-resistant genera. Moreover, the composition of rare genera in each sample was obviously different. Furthermore, a total of 18 potential pathogens were detected with Pseudomonas as the dominant genus, most of which were significantly reduced after disinfection. There were mainly positive interactions among potential pathogenic bacteria, with Enterococcus, Legionella and Vibrio as the hub genera as revealed by network analysis. Similar bacterial functions in both biofilm and water were observed with metabolism as the predominant bacterial function, while, human disease function only accounted for 1.07% of bacterial functions. These results highlighted the importance of continuous secondary chlorination for controlling biosafety of SWSS and identified the dissimilar responses of abundant and rare bacteria to the disinfection, as well as the co-occurrence patterns among potential pathogens, improving our understanding of bacterial communities in SWSS.

An Outbreak of Gastroenteritis Associated with GII.17 Norovirus-Contaminated Secondary Water Supply System in Wuhan, China, 2017.

A gastroenteritis outbreak occurred in a university in May, 2017, Wuhan, China. The epidemiological survey and pathogen analysis were conducted to identify the pathogen and control this outbreak. Feces or anal swabs from individuals, water, and swabs taken from tap surfaces of the secondary water supply system (SWSS) and foods were collected for the detection of viruses and pathogenic enteric bacteria by real-time RT-PCR and culture, respectively. Nucleotide sequences were determined by RT-PCR and direct sequencing. Genotyping, phylogenetic, and recombination analyses were conducted by a web-based genotyping tool, MEGA, and RDP4 programs, respectively. Of 144 individuals enrolled, 75 met the case definitions. The epidemic curve showed one peak of incidence suggesting the most probable spread of a single common source. In total, 33 specimens were collected before disinfection of the SWSS. Of these, norovirus was detected and identified as GII.P17-GII.17 with 100% nucleotide sequence identity among the strains detected in ten students (10/14), a maintenance worker (1/2) dealing with the SWSS, four water samples (4/8), and two swabs taken from tap surfaces (2/3). Pathogens including Vibrio cholerae, Salmonella, Shigella, Vibrio parahaemolyticus, Bacillus cereus, enteropathogenic Escherichia coli, rotavirus, astrovirus, and sapovirus were negative. The GII.17 strains in this outbreak clustered closely in the same branch of the phylogenetic tree, and slightly apart from the strains of other cities in China, neighboring countries and regions, European and American countries. This gastroenteritis outbreak was deduced to be attributed to GII.P17-GII.17 norovirus contamination of the SWSS.

Influence of secondary water supply systems on microbial community structure and opportunistic pathogen gene markers.

Secondary water supply systems (SWSSs) refer to the in-building infrastructures (e.g., water storage tanks) used to supply water pressure beyond the main distribution systems. The purpose of this study was to investigate the influence of SWSSs on microbial community structure and the occurrence of opportunistic pathogens, the latter of which are an emerging public health concern. Higher numbers of bacterial 16S rRNA genes, Legionella and mycobacterial gene markers were found in public building taps served by SWSSs relative to the mains, regardless of the flushing practice (P < 0.05). In residential buildings, genes of L. pneumomhila, Acanthamoeba and Vermamoeba vermiformis were primarily detected in tanks and taps compared to the mains. Long water retention time, warm temperature and loss of disinfectant residuals promoted microbial growth and colonization of potential pathogens in SWSSs. Varied levels of microbial community shifts were found in different types of SWSSs during water transportation from the distribution main to taps, highlighting the critical role of SWSSs in shaping the drinking water microbiota. Overall, the results provided insight to factors that might aid in controlling pathogen proliferation in real-world water systems using SWSSs.

Health inspection and monitoring results analysis on secondary water supply in Shanghai / 上海预防医学

[Objective] To investigate the quality of secondary water supply in Shanghai , in order to provide the basis for efficient management measures . [ Methods] Secondary water supply data were collected and analyzed from Shanghai drinking water health inspection and monitoring information system . [ Results] Cleaning and disinfection of secondary water supply facilities and water quality self -check and others were found to be low in pass rate .The drinking water quality of secondary water supply was lower . The main unqualified monitoring indexes were oxygen consumption , total number of bacteria and residual chlorine. [ Conclusion] Several problems exist in secondary water supply .By using Shanghai drinking water health inspection and monitoring information system , we can take effective measures to achieve sec-ondary water supply scientific supervision , then ensuring water safety .

Investigation of Legionella Pollutionin in Central Air Conditioning System and Secondary Water Supply System in Public Places in Jiangxi Province / 环境与健康杂志

Objective To konw the Legionella contamination in the central air condition system and secondary water supply system in the public places of Jiangxi province. Methods 145 water samples were collected from the public places with central air conditioning system and secondary water supply system, in July to September in 2005-2006. Bacteria culture, hemagglutination test and duplex PCR test were used to identify Legionella. Results 15 Legionella strains was isolated from 145 samples, the positive rate was 10.34%, 7 Legionella strains was isolated from 78 samples of central air conditioning system, the positive rate was 8.97%, 8 Legionella strains was isolated from 57 samples of secondary water supply system,the positive rate was 14.04%. Conclusion It is necessary to strengthen the surveillance of Legionella in central air conditioning system and secondary water supply system.

Hygienic Survey of Drinking Water Plants in Shanxi Province / 环境与健康杂志

Objective To know the hygienic condition of different kinds of drinking water plants in Shanxi Province.Methods In 2007,422 water plants and 2 083 secondary water supply units were selected and the information and data that provided by all Sanitation Institute for Health Inspection and Supervision in Shanxi Province were analyzed.Results The hygienic conditions of city's municipal administration water supply systems were the best.Total qualified rate of water quality was 97.67%.The hygienic conditions of rural school's homemade water supply systems were the worst,the qualified rates of all items in the program were the lowest.Most of them had no any analyst and laboratory for water quality test.Only 10.2% of them had water disinfection facilities.Total qualified rate of water quality was 75.32%.In most of water plants,the lack of water quality test facilities and disinfection facilities was one important problem in drinking water safety.In addition,the lack of clean and disinfection in secondary water supply systems was another problem.Conclusion The hygienic conditions of drinking water plans are unsatisfactory and should be improved in Shanxi Province.

Investigation on Contamination of Drinking Water Reservoir in a Hotel in Wuhan City / 环境与健康杂志

Objective To know the cause for contamination of drinking water in a hotel. Methods Samples were taken from the reservoir 1 h, 14 h, 22 h and 33 h after contamination and the perceptible character, chemical and bacteriological test were done by using the methods in Analytical Methods for Water and Sanitary Standard for Drinking Water Quality(2001). Results The turbidity increased at 14 h after contamination and the highest level reached 3.82 NTU. The residual chlorine in tap water from the reservoir was less than 0.05 mg/L, the total count of bacteria was 940 cfu/ml, the total coliform bacteria was more than 1 600 MPN/100 ml and fecal coliforms was 130 MPN/100 ml. Conclusion The contamination of drinking water in the investigated hotel is caused by drinking water reservoir leakage, so more attention must be paid to the contamination of drinking water reservoir.

Analysis on 60 Pollution Accidents of Municipal Water Distribution Network and Secondary Water Supply System / 环境与健康杂志

To understand the characteristics and causes of the pollution accidents of municipal water distribution network and secondary water supply system.Data on the pollution accidents of municipal water distribution network and secondary water supply system having occurred in recent 20 years were collected and analyzed. The main pollution type of municipal water distribution network and secondary water supply system was biological pollution,the amount of which took 73.3% of the total accidents.The pollution accidents mainly occured in schools or colleges and residential buildings offered by some enterprises to their members and families with an occurrence rate of 11.7%,besides residential quarters,enterprises and institutions.The main links of pollution were observed in municipal water distribution system(51.7%)and water storage tanks high and low lying(43.3%).The main causes of pollution accidents were the leakage and breakage facilities and mislink between the water pipes and sewage pipes, which resulted in formation of negative pressure.Siphonage and sewage flowing backward,in addition the poor sanitary protection facilities polluted by sewage and rubbish. It was the top priorities to establish special legal system,to enhence the preventive sanitary inspection

Investigation on Health Safety Status of Secondary Water Supply in Tongzhou District / 环境与健康杂志

Objective To investigate the drinking water quality of secondary water supply in Tongzhou District, Beijing in order to establish a data monitoring management system. Methods The uniform questionnaires were used for the on-the-spot investigation at secondary water supply units in the whole district, which included secondary water supply facility situations, environmental sanitary conditions and health management and so on. At the same time, municipal water and secondary supply water were tested. Results 48 units of secondary water supply were investigated. In this investigation, the main systems of secondary water supply were the low water tank added frequency conversion pump(accounts for 77.1%) and the inverter constant pressure water supply system with negative pressure(accounts for 14.3%). According to the hygienic requirements, the unqualified rate of water tank structure, disinfection facility and water tank room were 81.0%, 73.3% and 87.3% respectively; besides, 39.6% of the units used the invalid hygienic licenses, 43.5% of the water managers had no health certificates, and 54.5% of the units had never cleaned their water tanks. The total qualification rate of the secondary water supply was 66.7%. The main items that were not up to the standard were ammonia-nitrogen, free chlorine, recognizable objects with naked eyes, total bacteria count and turbidity. For the different water material, the qualification rate showed a significant difference(P=0.023). Conclusion The drinking water quality of the secondary water supply is lower than before and the preventive hygiene supervision and evaluation is comparatively delayed in the investigated district.

Analysis on Sanitation of Secondary Drinking Water Supply System in Public Places / 环境与健康杂志

Objective To Cenderstand the sanitation status of secondary drinking water supply system of public places. Methoods The sanitation of secondary drinking water supply system was investigated by on_site survey method and the sanitary quality of water samples were determined. Results The over_standard rates contents of Fe and total coliformz of water samples of secondary water supply system significantly increased compared with the related levels of tap water of municipal water supply. The unqualified rate of free residual chorine of water sample from secondary water supply system reached 54.55%. Conclusions The equipments for secondary water supply were obsolete and unretional design. The sanitary quality of secondary water supply was also affected by geological structure easily.