The biological threat to U.S. water supplies: Toward a national water security policy

In addition to providing potable drinking water, U.S. water systems are critical to the maintenance of many vital public services, such as fire suppression and power generation. Disruption of these systems would produce severe public health and safety risks, as well as considerable economic losses. Thus, water systems have been designated as critical to national security by the U.S. government. Previous outbreaks of waterborne disease have demonstrated the vulnerability of both the water supply and the public's health to biological contamination of drinking water. Such experiences suggest that a biological attack, or even a credible threat of an attack, on water infrastructure could seriously jeopardize the public's health, its confidence, and the economic vitality of a community. Despite these recognized vulnerabilities, protecting water supplies from a deliberate biological attack has not been sufficiently addressed. Action in this area has suffered from a lack of scientific understanding of the true vulnerability of water supplies to intentional contamination with bioweapons, insufficient tools for detecting biological agents, and a lack of funds to implement security improvements. Much of what is needed to address the vulnerability of the national water supply falls outside the influence of individual utilities. This includes developing a national research agenda to appropriately identify and characterize waterborne threats and making funds available to implement security improvements.     

Annual cancer risks from chemicals in North Carolina community water systems

Motivated partly by concerns about cancer, the U.S. Congress in 1986 amended the Safe Drinking Water Act (SDWA) by requiring that community water systems monitor 81 chemicals and remove those detected at concentrations above health-based standards. No prior research has used the resulting 30 years of monitoring data to analyze cancer risks from chemicals in US drinking water. To fill this gap, this paper uses chemical monitoring data from North Carolina's (NC's) 2,120 community water systems along with a risk assessment approach commonly applied in global burden of disease studies to quantify cancer risks of regulated chemicals in drinking water. The results indicate that 0.30% of NC cancer deaths are attributable to regulated drinking water contaminants and that the average annual individual risk is 7.2 × 10^?6. More than 99% of this risk arises from disinfection by-products, with the remaining risk mostly attributable to arsenic and alpha particle radiation. In no water system does the combined risk from chemicals other than disinfection by-products, arsenic, or alpha particles exceed 10^?4. The results suggest that regulated chemicals pose very low cancer risks and that risks from chemicals other than disinfection by-products, arsenic, and alpha particles are negligible in NC community water systems.     

Assessing Children's Exposures and Risks to Drinking Water Contaminants: A Manganese Case Study

Background: Compared to adults, children maybe more highly exposed to toxic substances in drinking water because they consume more water per unit of body weight. The U.S. Environmental Protection Agency (USEPA) has developed new guidance for selecting age groups and age-specific exposure factors for assessing children's exposures and risks to environmental contaminants. Research Aim: To demonstrate the application and importance of applying age-specific drinking water intake rates, health reference values, and exposure scenarios when assessing drinking water exposures because these approaches illustrate the potential for greater potential for adverse health effects among children. Methods: manganese, an essential nutrient and neurotoxicant, was selected as a case study and chemical of potential concern for children's health. A screening-level risk assessment was performed using age-specific drinking water intake rates and manganese concentrations from U.S. public drinking water systems. Results: When age-specific drinking water intake rates are used to calculate dose, formula-fed infants receive the highest dose of manganese from drinking water compared to all other age groups. Estimated hazard quotients suggest adverse health effects are possible. Use of USEPA's standardized childhood age groups and childhood exposure factors significantly improves the understanding of childhood exposure and risks.     

Escherichia coli: the best biological drinking water indicator for public health protection

Public health protection requires an indicator of fecal pollution. It is not necessary to analyse drinking water for all pathogens. Escherichia coli is found in all mammal faeces at concentrations of 10 log 9(-1), but it does not multiply appreciably in the environment. In the 1890s, it was chosen as the biological indicator of water treatment safety. Because of method deficiencies, E. coli surrogates such as the 'fecal coliform' and total coliforms tests were developed and became part of drinking water regulations. With the advent of the Defined Substrate Technology in the late 1980s, it became possible to analyse drinking water directly for E. coli (and, simultaneously, total coliforms) inexpensively and simply. Accordingly, E. coli was re-inserted in the drinking water regulations. E. coli survives in drinking water for between 4 and 12 weeks, depending on environmental conditions (temperature, microflora, etc.). Bacteria and viruses are approximately equally oxidant-sensitive, but parasites are less so. Under the conditions in distribution systems, E. coli will be much more long-lived. Therefore, under most circumstances it is possible to design a monitoring program that permits public health protection at a modest cost. Drinking water regulations currently require infrequent monitoring which may not adequately detect intermittent contamination events; however, it is cost-effective to markedly increase testing with E. coli to better protect the public's health. Comparison with other practical candidate fecal indicators shows that E. coli is far superior overall.     

Towards a triple bottom-line sustainability assessment of the U.S. construction industry

Purpose

The construction industry has considerable impacts on the environment, economy, and society. Although quantifying and analyzing the sustainability implications of the built environment is of great importance, it has not been studied sufficiently. Therefore, the overarching goal of this study is to quantify the overall environmental, economic, and social impacts of the U.S. construction sectors using an economic input–output-based sustainability assessment framework.

Methods

In this research, the commodity-by-industry supply and use tables published by the U.S. Bureau of Economic Analysis, as part of the International System of National Accounts, are merged with a range of environmental, economic, and social metrics to develop a comprehensive sustainability assessment framework for the U.S. construction industry. After determining these sustainability assessment metrics, the direct and indirect sustainability impacts of U.S construction sectors have been analyzed from a triple bottom-line perspective.

Results

When analyzing the total sustainability impacts by each construction sector, “Residential Permanent Single and Multi-Family Structures" and "Other Non-residential Structures" are found to have the highest environmental, economic, and social impacts in comparison with other construction sectors. The analysis results also show that indirect suppliers of construction sectors have the largest sustainability impacts compared with on-site activities. For example, for all U.S. construction sectors, on-site construction processes are found to be responsible for less than 5 % of total water consumption, whereas about 95 % of total water use can be attributed to indirect suppliers. In addition, Scope 3 emissions are responsible for the highest carbon emissions compared with Scopes 1 and 2. Therefore, using narrowly defined system boundaries by ignoring supply chain-related impacts can result in underestimation of triple bottom-line sustainability impacts of the U.S. construction industry.

Conclusions

Life cycle assessment (LCA) studies that consider all dimensions of sustainability impacts of civil infrastructures are still limited, and the current research is an important attempt to analyze the triple bottom-line sustainability impacts of the U.S. construction sectors in a holistic way. We believe that this comprehensive sustainability assessment model will complement previous LCA studies on resource consumption of U.S. construction sectors by evaluating them not only from environmental standpoint, but also from economic and social perspectives.     

Biological approaches for addressing the grand challenge of providing access to clean drinking water

The U.S. National Academy of Engineering (NAE) recently published a document presenting "Grand Challenges for Engineering". This list was proposed by leading engineers and scientists from around the world at the request of the U.S. National Science Foundation (NSF). Fourteen topics were selected for these grand challenges, and at least seven can be addressed using the tools and methods of biological engineering. Here we describe how biological engineers can address the challenge of providing access to clean drinking water. This issue must be addressed in part by removing or inactivating microbial and chemical contaminants in order to properly deliver water safe for human consumption. Despite many advances in technologies this challenge is expanding due to increased pressure on fresh water supplies and to new opportunities for growth of potentially pathogenic organisms.     

Variations of bacterial 16S rDNA phylotypes prior to and after chlorination for drinking water production from two surface water treatment plants

We examined the variations of bacterial populations in treated drinking water prior to and after the final chlorine disinfection step at two different surface water treatment plants. For this purpose, the bacterial communities present in treated water were sampled after granular activated carbon (GAC) filtration and chlorine disinfection from two drinking water treatment plants supplying the city of Paris (France). Samples were analyzed after genomic DNA extraction, polymerase chain reaction (PCR) amplification, cloning, and sequencing of a number of 16S ribosomal RNA (rRNA) genes. The 16S rDNA sequences were clustered into operational taxonomic units (OTUs) and the OTU abundance patterns were obtained for each sample. The observed differences suggest that the chlorine disinfection step markedly affects the bacterial community structure and composition present in GAC water. Members of the Alphaproteobacteria and Betaproteobacteria were found to be predominant in the GAC water samples after phylogenetic analyses of the OTUs. Following the chlorine disinfection step, numerous changes were observed, including decreased representation of Proteobacteria phylotypes. Our results indicate that the use of molecular methods to investigate changes in the abundance of certain bacterial groups following chlorine-based disinfection will aid in further understanding the bacterial ecology of drinking water treatment plants (DWTPs), particularly the disinfection step, as it constitutes the final barrier before drinking water distribution to the consumer’s tap.     

Analysis of structure and composition of bacterial core communities in mature drinking water biofilms and bulk water of a citywide network in Germany

The bacterial core communities of bulk water and corresponding biofilms of a more than 20-year-old drinking water network were compared using 16S rRNA single-strand confirmation polymorphism (SSCP) fingerprints based on extracted DNA and RNA. The structure and composition of the bacterial core community in the bulk water was highly similar (>70%) across the city of Braunschweig, Germany, whereas all biofilm samples contained a unique community with no overlapping phylotypes from bulk water. Biofilm samples consisted mainly of Alphaproteobacteria (26% of all phylotypes), Gammaproteobacteria (11%), candidate division TM6 (11%), Chlamydiales (9%), and Betaproteobacteria (9%). The bulk water community consisted primarily of Bacteroidetes (25%), Betaproteobacteria (20%), Actinobacteria (16%), and Alphaproteobacteria (11%). All biofilm communities showed higher relative abundances of single phylotypes and a reduced richness compared to bulk water. Only biofilm communities sampled at nearby sampling points showed similar communities irrespective of support materials. In all of our bulk water studies, the community composition determined from 16S rRNA was completely different from the 16S rRNA gene-based community composition, whereas in biofilms both molecular fractions resulted in community compositions that were similar to each other. We hypothesize that a higher fraction of active bacterial phylotypes and a better protection from oxidative stress in drinking water biofilms are responsible for this higher similarity.     

Identification and phylogeny of eukaryotic 18S rDNA phylotypes detected in chlorinated finished drinking water samples from three Parisian surface water treatment plants

Aims:  We performed a preliminary assessment of the eukaryotic 18S rDNA diversity present in finished drinking water samples from three different surface water treatment plants supplying water to the city of Paris (France).
Methods and Results:  A molecular analysis was performed on a sample from each site based on sequencing of PCR amplified and cloned 18S ribosomal RNA genes. Overall, the 18S rDNA sequences combined from all samples could be affiliated to the Amoebozoa (20·8% of the phylotypes), Ciliophora (25%), Metazoa (33·3%), Fungi (8·3%), Cercozoa (4·2%) and unclassified eukaryotes (8·3%) groups.
Conclusions:  The 18S rDNA sequences affiliated to the Amoebozoa, Ciliophora and Metazoa lineages were found to be the most abundant phylotypes observed in the drinking water samples. Phylotypes found to be present in two, or all three, samples (41·7% of the total) may represent groups with members adapted to drinking water treatment plant (DWTP) ecosystem conditions.
Significance and Impact of the Study:  This study shows that finished drinking water can contain 18S rDNA sequences representing a variety of eukaryotic taxa. Further research is needed to better characterize the eukaryotic biodiversity of DWTPs and the effects of the finished drinking water diversity on the downstream water distribution network.     

A Probabilistic Assessment of Household Exposures to MTBE from Drinking Water

The oxygenate methyl tertiary butyl ether (MTBE) has been added to reformulated gasoline in the U.S. to meet national ambient air quality standards. Although MTBE has provided significant health benefits in terms of reduced criteria and toxic air pollutants, detections of MTBE in some groundwater and drinking water sources have raised concerns about potential environmental contamination and human exposures. In this paper, we examine the frequency and concentration of MTBE detections in drinking water sources in California from 1995 to 1999, and provide a preliminary analysis of the distribution of household exposures to MTBE from water-related activities. Using published data on the toxicity and possible cancer hazard posed by MTBE, we estimate the likely cancer and non-cancer risks for the general population in California from past and potential future MTBE exposures. More highly exposed subgroups were also addressed. Our findings indicate that less than 2% of all sampled drinking water sources in California had detectable levels of MTBE in 1999, with average MTBE drinking water concentrations ranging from 0.09 to 4.9?ppb for this year. Both the detection rate for MTBE and average MTBE concentrations have remained relatively stable since 1995, despite increased sampling of drinking water sources in California. The probabilistic exposure analysis suggests that drinking water exposures to MTBE are unlikely to pose a significant health risk for the general population or more highly exposed individuals in California.     

Microbial biogeography of drinking water: patterns in phylogenetic diversity across space and time

In this study, we collected water from different locations in 32 drinking water distribution networks in the Netherlands and analysed the spatial and temporal variation in microbial community composition by high‐throughput sequencing of 16S rRNA gene amplicons. We observed that microbial community compositions of raw source and processed water were very different for each distribution network sampled. In each network, major differences in community compositions were observed between raw and processed water, although community structures of processed water did not differ substantially from end‐point tap water. End‐point water samples within the same distribution network revealed very similar community structures. Network‐specific communities were shown to be surprisingly stable in time. Biofilm communities sampled from domestic water metres varied distinctly between households and showed no resemblance to planktonic communities within the same distribution networks. Our findings demonstrate that high‐throughput sequencing provides a powerful and sensitive tool to probe microbial community composition in drinking water distribution systems. Furthermore, this approach can be used to quantitatively compare the microbial communities to match end‐point water samples to specific distribution networks. Insight in the ecology of drinking water distribution systems will facilitate the development of effective control strategies that will ensure safe and high‐quality drinking water.     

Perfluorooctanoic Acid (PFOA): Environmental Sources,Chemistry, Toxicology,and Potential Risks

Attention regarding perfluoroalkyl and polyfluoroalkyl substances (PFAS) has increased in recent years, due to recognition of widespread environmental presence, recognition of a chemical structure that confers resistance to degradation, and reported health concerns. Historical common exposure sources include food, drinking water, occupational circumstances, and products in commerce (e.g., carpeting, clothing, paper products). Early-2000’s data showed perfluorooctanoic acid (PFOA) was present in blood samples from nearly all the U.S. general population (>99%). Alterations in industrial manufacturing processes, increased regulatory scrutiny, and advanced water treatment options have reduced the reported human body burden of PFAS in the U.S., including for PFOA. Human serum concentrations of PFOA, which do not identify the source(s) of exposure, have exhibited a substantial decrease (~63%) between the 1999–2000 and the 2013–2014 NHANES monitoring by the Centers for Disease Control and Prevention (CDC). With respect to both noncancer and potential cancer effects that may be associated with reported serum levels of PFOA, conclusions regarding an absence of effects, or insufficient information to suggest adverse effects, prevent a consistent conclusion about the occurrence and magnitude of human health effects. In the last several years, a number of state and federal agencies have developed health advisories or guideline values for drinking water exposure that are in the sub-ppb range. In 2016, a USEPA Health Advisory of 0.07 ppb was released, which stands in contrast to 2016 Health-based Values from Health Canada ranging from 0.2 ppb (PFOA) to 30 ppb, and a few other U.S. states with values even less than that of USEPA (e.g., MN, NJ, VT). Further work is necessary to distinguish in transparent fashion between drinking water levels that intentionally are set on a conservative basis to protect human health vs exposure levels that may be associated with tangible adverse effects.     

Are There Health Risks from the Migration of Chemical Substances from Plastic Pipes into Drinking Water? A Review

Plastic pipes used to convey hot and cold drinking water are synthetic polymers containing numerous additives that enhance durability, impact strength, and toughness, and resist material degradation. Although some research studies have been conducted to evaluate the type and levels of chemical substances migrating from polymeric materials into drinking water, the potential adverse health effects associated with these compounds in potable water have not been described. This review evaluates the literature on the occurrence of regulated and unregulated substances in drinking water related to the use of plastic pipes, characterizes potential health hazards, and describes uncertainties associated with human health and exposure in need of further research. Of particular public health concern is the potential for sensitive populations to be exposed to short-term elevations in leachates during critical periods, and for co-occurring leachates targeting the same organ(s) and/or sharing a common mode of toxic action to have additive or synergistic effects. Contaminants are measured in the distribution system, not at the tap where human exposure actually occurs. For increased health protection, it is important to identify compounds that migrate from plastic pipes into drinking water and to better quantify human exposures and health hazards to these substances and their degradates.     

饮用水氟污染控制原理与技术

天然地球化学过程导致全球范围内广泛存在地下水氟污染,饮用水氟超标人口达5亿.控制以高氟地下水为饮用水源的氟污染及其健康风险,成为饮用水质安全保障的核心问题之一.全世界在饮用水除氟方面做了大量努力,但成效十分有限.在此背景下,深刻认识氟污染形成机制与地球化学特征,结合地理信息、遥感等手段预测区域风险水平,优先考虑“更换水源”,仍是饮用水氟污染控制的重要策略.此外,在研究层面上,应以净水药剂、环境功能材料创新为基础,以混凝沉淀、吸附、膜分离为重要技术方向,开发适用于发展中国家或欠发达地区的高效、经济、方便、稳定的除氟关键技术和成套设备;在工程应用层面上,应加强饮用水除氟设施设计、建设、运行与监管,确保设施长期稳定运行,实现工程效益.     

Mitochondrial Replacement Techniques

In this article, I draw on research carried out in Europe, primarily in Germany, on patients’ and scientists’ perspectives on mitochondrial replacement techniques (MRTs) in order to explore some of the complexities related to collective representation in health governance, which includes the translation of emerging technologies into clinical use. Focusing on observations, document analyses, and interviews with eight mitochondrial disease patient organization leaders, this contribution extends our understanding of the logic and meanings behind the ways in which patient participation and collective representation in health governance initiatives take shape. My findings highlight the ways in which a commitment to a global mitochondrial disease patient community and a sense of patient solidarity influence expressions of support with regard to legalizing mitochondrial replacement techniques. My analyses illustrate how normative practices and expectations of participatory governance potentially foreclose opportunities for sustained collective patient engagement with the complex ethical, social, and political dimensions of emerging technologies and may silence diverse and potentially dissenting embodied and lived responses to the prospects of particular technological developments.     

Physical mobility under stay-at-home orders: A comparative analysis of movement restrictions between the U.S. and Europe

During the COVID-19 pandemic, both the U.S. and Europe have issued movement restrictions with the exception of visits to essential services, including groceries and pharmacies. Using Google's data on community mobility, I employ an event-study design to compare the effects of movement restrictions on physical mobility in the U.S. and Europe. I find that compared to Europe, the U.S. has higher levels of mobility related to visits to groceries and pharmacies and lower levels of the residential presence relative to baseline values, and the differences are not only statistically significant but also of large magnitudes. Such differences in post-restriction mobility are still significant between Europe and the U.S.’ early epicenters of COVID-19. The main results of this paper are robust to changes in samples and specifications. These findings suggest that movement restrictions appear to be less effective in the U.S., which have useful implications for health policy evaluation, pandemic forecasting, and economic recovery.     

Historical drinking water contamination at Camp Lejeune: Regulatory risk assessor and personal perspectives

Historical concentrations of trichloroethylene (TCE) and other chemicals in drinking water at the U.S. Marine Corps Base at Camp Lejeune, NC, were sufficiently elevated to raise potential health concerns. The 1952–1984 mean TCE concentration (138 µg/L) exceeded the U.S. Environmental Protection Agency's (USEPA's) current maximum contaminant level (MCL) of TCE by 28-fold, with the corresponding dose (3.9E–03 mg/kg-day) exceeding all three candidate USEPA reference dose (RfD) values by 8- to 11-fold. Today, TCE hazard quotients (HQs) of 8–11 compel immediate action by USEPA. The mean dose also exceeds the supporting RfD values for toxic nephropathy and increased kidney weight, as well as the point of departure (POD) for toxic nephropathy. Furthermore, the estimated doses for 34% of the 9-month rolling averages exceed the POD for the highest RfD value for fetal heart defects. The incidences of nephropathy and fetal heart defects should be thoroughly evaluated among those who were exposed. Long-term follow-up will be required to assess potential health effects for the 500,000 to 1 million people who may have used the contaminated water at Camp Lejeune or were exposed in utero. This should serve as a cautionary tale for the thousands of Department of Defense sites across the USA (and other similarly contaminated sites elsewhere in the world) that are commonly contaminated with chemicals such as those at Camp Lejeune, where necessary sampling should be conducted to identify and mitigate any likely ongoing (or future) exposures of potential health concern.     

Why Would Anyone Object? An Exploration of Social Aspects of Phytoremediation Acceptability

Referee: Mr. Peter Siebach, Environmental Engineer, U.S. Department of Energy, Chicago Operations Office, 9800 South Cass Avenue, Argonne, IL 60439 Phytoremediation comprises a suite of promising cleanup technologies that use plants to remove or contain contaminants in soil and water. To be deployed, phytoremediation must be both technically and socially acceptable. This article explores the potential social acceptability of phytoremediation options proposed for use at specific sites and describes the conceptual framework that guides our exploration. The framework, called PACT (Public Acceptability of Controversial Technologies), consists of Dialog, Technology, Constituent, and Context dimensions. It posits that remediation decision making is a social process informed by scientific and technical information, rather than a science- or technology-driven process. Although empirical data are scarce, applying PACT shows that a number of issues have the potential to impose conditions on the social acceptability of phytoremediation, and that some issues could lead to outright rejection. Further, because many of these issues concern values and goals, they cannot be resolved simply by providing better or more detailed technical information about phytoremediation. PACT is instructive in showing how even seemingly benign or desirable technologies such as phytoremediation have the potential to generate public controversy, delineating issues in ways that can help lead to their resolution.     

Suffering from Water: Social Origins of Bodily Distress in a Mexican Community

This article is an ethnographic analysis of what it means to "suffer from water." Using a critical medical anthropology approach, the study examines how residents living in a foothill community of the Valley of Mexico experience bodily distress associated with water scarcity. Data for the study come from participant-observation of domestic water use and community drinking water management as well as interviews with local civil and religious officials who monitor the water distribution system. While the community discourse on suffering from water does not correspond to biomedical categories of illness, it does speak to the physical and emotional hardships and the social conditions that limit residents' access to an adequate supply of domestic water. By taking a broad view of water-related suffering, the study reveals some of the efforts made by people to address what they consider to be the social origins of their bodily distress.     

Detection and enumeration of coliforms in drinking water: current methods and emerging approaches.

The coliform group has been used extensively as an indicator of water quality and has historically led to the public health protection concept. The aim of this review is to examine methods currently in use or which can be proposed for the monitoring of coliforms in drinking water. Actually, the need for more rapid, sensitive and specific tests is essential in the water industry. Routine and widely accepted techniques are discussed, as are methods which have emerged from recent research developments.Approved traditional methods for coliform detection include the multiple-tube fermentation (MTF) technique and the membrane filter (MF) technique using different specific media and incubation conditions. These methods have limitations, however, such as duration of incubation, antagonistic organism interference, lack of specificity and poor detection of slow-growing or viable but non-culturable (VBNC) microorganisms. Nowadays, the simple and inexpensive membrane filter technique is the most widely used method for routine enumeration of coliforms in drinking water.The detection of coliforms based on specific enzymatic activity has improved the sensitivity of these methods. The enzymes beta-D galactosidase and beta-D glucuronidase are widely used for the detection and enumeration of total coliforms and Escherichia coli, respectively. Many chromogenic and fluorogenic substrates exist for the specific detection of these enzymatic activities, and various commercial tests based on these substrates are available. Numerous comparisons have shown these tests may be a suitable alternative to the classical techniques. They are, however, more expensive, and the incubation time, even though reduced, remains too long for same-day results. More sophisticated analytical tools such as solid phase cytometry can be employed to decrease the time needed for the detection of bacterial enzymatic activities, with a low detection threshold.Detection of coliforms by molecular methods is also proposed, as these methods allow for very specific and rapid detection without the need for a cultivation step. Three molecular-based methods are evaluated here: the immunological, polymerase chain reaction (PCR) and in-situ hybridization (ISH) techniques. In the immunological approach, various antibodies against coliform bacteria have been produced, but the application of this technique often showed low antibody specificity. PCR can be used to detect coliform bacteria by means of signal amplification: DNA sequence coding for the lacZ gene (beta-galactosidase gene) and the uidA gene (beta-D glucuronidase gene) has been used to detect total coliforms and E. coli, respectively. However, quantification with PCR is still lacking in precision and necessitates extensive laboratory work. The FISH technique involves the use of oligonucleotide probes to detect complementary sequences inside specific cells. Oligonucleotide probes designed specifically for regions of the 16S RNA molecules of Enterobacteriaceae can be used for microbiological quality control of drinking water samples. FISH should be an interesting viable alternative to the conventional culture methods for the detection of coliforms in drinking water, as it provides quantitative data in a fairly short period of time (6 to 8 h), but still requires research effort.This review shows that even though many innovative bacterial detection methods have been developed, few have the potential for becoming a standardized method for the detection of coliforms in drinking water samples.