Abstract

Safe drinking water is a product that is free of contaminants which pose short and long-term risks to the consumers’ well-being. It is an indispensable resource that safeguards public health and engenders sustainable economic development. We conducted a systematic review of journal article published between 2010-2020 to (a) identify, appraise, and synthesize the best available evidence for the factors that affect the quality of drinking water in the United States of America (b) make appropriate recommendations to improve the quality of drinking water. Eligible studies were systematically reviewed and selected for analysis from searches of 21,042 publications identified from six databases. We analyzed factors affecting quality of ground water, surface water, water treatment plants, water distribution systems, tap water and bottled water. 201 studies were included in this review, and more than half were published between 2016-2020. The major water contaminant identified from this review was chemical waste from industries (33.3%), followed by pathogens (32.3%), metals and naturally occurring substances (23.9%), pharmaceuticals (9.0%), natural gas and oil (1.0%) and biogenic substance (0.5%). Therefore, factors affecting the quality of water include industrial activities, pathogens especially from fecal contamination of water, agricultural practices, naturally occurring substances, pharmaceutical substances, and natural disasters. There is need to enforce regulations that protect all sources of drinking water from pollution by industrial effluents and other anthropogenic sources. Improvements in water treatment processes and continuous water monitoring, especially in the rural areas, will help to improve the quality of drinking water in the United States. Systematic review registration: The systematic review protocol was registered (CRD42021271183) and is published on PROSPERO.

1. Introduction

Water is an important substance to human beings and other living organisms on earth ¹. It is an indispensable natural resource that is critical for human health, functioning ecosystems, and sustainable socioeconomic development ². It covers two-thirds of the earth’s surface in a form that is largely unsafe for human consumption because it contains microbial, chemical, and other contaminants that are inimical to human health. The freshwater which human beings process for drinking is 2.7% of the available water on earth and only 1% of this is accessible to humans because it is hidden in deep aquifers and glaciers ³. The various sources of water humans use for drinking purposes include groundwater, rainwater, streams, aquifers, glaciers, and natural springs. The knowledge of these sources of water and pragmatic efforts towards protecting them from all kinds of pollution are germane to the management of water resources and provision of safe drinking water for consumers ⁴.

Safe drinking water emanates from public water systems, private wells or bottled water factories and is delivered to consumers in a manner suitable for drinking, domestic use, and personal hygiene ⁵. According to the World Health Organization (WHO) 2020 report, safe drinking water is a form of water that has undergone treatment and does not pose any significant risk to the health of consumers in the immediate or long term ⁶. It is the outcome of a multistage process that ensures the removal of contaminants from freshwater, leading to the production of high-quality water that is safe for human consumption ⁷. Public and private water systems take raw water through the processes of screening, chemical addition, coagulation, flocculation, sedimentation, filtration, disinfection, storage, and distribution to the consumers ⁸. These processes require appropriate techniques and modern technologies that can enhance the capacities of water treatment plants to produce safe water in quantities that meet the community needs and qualities that measure up to regulatory requirements ⁹. Safe drinking water has characteristics that usually fall within three categories: physical, chemical, and microbiological. Physically, water must be odorless, tasteless, colorless, and turbid free. Chemically, safe water is required to be free from toxic substances, contaminants, excess minerals, divalent ions, organic matters, and a pH of 6.5-8.5. It must be free of pathogens and radioactive substances The Table 1 below shows the standard values for safe drinking water according to the WHO and United States Environmental Protection Agency ^{10, 11} (USEPA).

There is a plethora of literature describing factors that affect the quality of safe drinking water. These factors are events and situations that result in the contamination of water from the water source to the water treatment plants, through decaying water distribution infrastructures and household water storage facility ¹². For example, the improperly disposed of industrial chemicals, animal wastes, pesticides, human wastes, and naturally occurring substances can all contaminate ground and surface water ¹³. Long and colleagues reported that surface and underground water sources are often polluted during the rainy season due to increase in the soil table water and human activities. This would lead to an increase in the level of water contaminants like nitrates, pesticides, and fecal coliforms which are then transferred to the treatment plant ¹⁴. The water treatment plants are designed to eliminate harmful substances, contaminants, and disease-carrying pathogens from the raw water ¹⁵. However, a breach in the integrity of the processes mentioned earlier can result in the distribution of water contaminated with antibiotics, pesticides, and other unacceptable elements to the community ¹⁶.

Furthermore, the distribution of treated water using ageing pipeline often cause deterioration in taste, color, odor, and turbidity which compromise the quality of water pumped into the community from the treatment plants ¹⁷. A recent and typical example is the Flint, Michigan water crisis in 2014. This resulted in leaching of lead and other metals from the city's aging pipes into the water supplied into homes and businesses thereby exposing around 100,000 residents to elevated lead levels with their health consequences ¹⁸. Household water storage systems and plumbing facilities can also constitute a potential source of water contamination. A cross-sectional household survey of 800 households was conducted across three informal peri-urban neighborhood which reported that most households drinking water sample had fecal contamination (67%), defined by the presence of colony forming units of the fecal indicator bacteria enterococci ¹⁹.

The unwavering determination and efforts of the United State government to provide safe drinking water for the citizens have brought some remarkable progress across the States but the momentum must be sustained. Globally, disparities and inequalities exist in access to safe drinking water between towns and cities, developing and developed countries, the gap is reducing gradually. In Sub-Saharan Africa, where the rate of access is lowest, household access to safe drinking water is increasing steadily ²⁰ The United Nation General assembly sustainable development goals in 2010 and 2015 recognized the rights of individuals to safe, acceptable, affordable, and accessible water for both domestic and personal use ²¹. Despite these interventions, studies show that 140 million are exposed to unsafe levels of arsenic element and 2 billion people drink water source contaminated with feces, which poses significant health risk by increasing the occurrence of water borne diseases such as poliomyelitis and dysentery with estimated 829,000 diarrheal deaths annually.

In view of the foregoing, this research is imperative because safe drinking water is critical to human survival and a major factor affecting human health. According to WHO, poor access to safe drinking water, improper hygiene practices, and unimproved sanitation account for four percent of all deaths and 5.7 percent of all ill health and disabilities in the world. In addition, there are communities and individuals who are unaware of their exposure to health risks from water contaminated with lead, toxic chemicals, microbes, and others. This review focused on factors affecting the quality of drinking water in the United States. Therefore, the objectives of this review are to (i) identify, appraise, and synthesize the best available evidence for the factors that affect the quality of safe drinking water in the United States of America (ii) make appropriate recommendations to improve the quality of drinking water.

2. Materials and Methods

We followed the reporting guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analysis for Protocols 2015 and guidance for dissemination of results ²³. The study protocol was registered in the International Prospective Register of Systematic Reviews Database (PROSPERO) (available at https://www.crd.york.ac.uk/prospero) in August 2021 with registration number CRD4202127118.

This study systematically reviewed journal articles on factors affecting the quality of drinking water in the United States published between 2010 and 2020. A University Librarian developed the search strategy in MEDLINE Complete. The initial search strategy was tested and refined by sampling search results and applying proposed inclusion and exclusion criteria. Once completed, the search strategy was translated to five other databases. Final searching was completed in MEDLINE Complete (Ebsco interface), CINAHL Complete (Ebsco interface) Web of Science Core Collection, ABI/INFORM (ProQuest interface), ProQuest Agricultural & Environmental Science Collection, and COMPENDEX (Engineering Village interface). Search terms related to drinking water and water quality were used and an extensive list of foreign countries were used as excluding keywords. The searching of databases and screening of articles were conducted between November 2021 and February 2022. The list of complete search strategy (Table 2), list of databases that were searched (Table 3) and Prisma flow diagram for this study (Figure 1) are presented below.

Retrieved articles were imported into Zotero where duplicates were removed. The deduplicated set of articles was then uploaded to Rayyan where two authors performed title and abstract screening and removed ineligible articles. The remaining papers were downloaded for eligibility assessment and data extraction. The inclusion criteria include (i) peer reviewed primary studies published in English language from the United States of America. (ii) Investigation time: 2010–2020 (iii) studies that focused on drinking water and reported factor(s) affecting quality of safe drinking water (iv) study design such as randomized controlled trials RCTs, quasi-RCT, and experimental design were considered.

Exclusion criteria included: (i) studies not related to the research topic (ii) studies not published within the year 2010-2020 (iii) Commentaries, case-controls, cohort study, reviews, opinion pieces, proceedings of conferences, editorials, and non-peer reviewed reports.

Titles and abstracts of search results were screened by two independent reviewers for methodological validity prior to inclusion in the review using standardized critical appraisal instruments from the Joanna Briggs Institute (JBI) Critical appraisal checklist for systematic review and research synthesis ²⁴. Disagreements that ensued between them were resolved through discussion with a third reviewer.

Data extractions were conducted independently by two authors and disagreements resolved by a third author. The Data extracted covered the following parameters: author, year of publication, study aim, sampling site/location, rural/urban, State, sampling year/period, study design, water contaminants, sampling point, author and reviewers’ conclusions, and factors affecting quality of drinking water.

The information listed in section 2.5 above were entered into a Microsoft Excel database. The main outcomes from quantitative evaluations were extracted, summarized, and discussed.

3. Results

A total of 21,042 publications were identified from six databases, out of which 8,320 were duplicates and 12,332 were excluded based on title and abstract. A total of 390 articles were selected for full text review. The most common reasons for exclusion were that the study used secondary or existing dataset for analysis (n=101), used research designs like reviews, case controls or retrospective cohort studies (n= 50) and did not focus on quality of drinking water (n=38). Finally, 201 publications were included in this systematic review. The results of this review are organized into characteristics of literature included, factors affecting the quality of surface water, groundwater, water at the treatment plants, water during distribution and at household levels.

Table 4 and Table 5 below summarized the characteristics of the 201 articles and the excel sheet containing the list of the articles reviewed in this study. All the included articles identified one or more contaminants affecting the quality of water in the United States. More than half of the articles (55.7%) were published between 2016-2020. The articles sampled and reported water situation in the Northeast (24.4%), Midwest (22.9%), West (16.4%) and South (14.9%) regions of the United States. Figure 2 below present a map of the United States showing sampling sites, location, and States. In this review, the states with the highest number of publications were Pennsylvania (6.5%), California (5.5%) and Colorado (5.0%) while 20.9% of the articles sampled water across multiple states. The setting reported most by the authors was urban (71.1%), followed by urban & rural (17.5%), and rural (11.4%). The study design used by most of the authors was inductively coupled plasma spectrometry, ICP-MS (23.4%), followed by liquid chromatography mass tandem spectrometry (20.4%), quantitative polymerase chain reaction (16.9%), gas chromatography capillary column (7.0%), DNA Sequencing (12.0%), culture-based method (3.0%) and other methods (17.3%).

Majority of the articles sampled and analyzed water from ground water (31.5%), followed by tap water (28.6%), surface water (27.8%), water treatment plant (9.1%), bottled water (2.5%) and distribution system (0.4%). The contaminants that were identified can be categorized into chemicals (33.3%), pathogens (32.3%), metals (23.9%), pharmaceuticals (9%), natural gas and oil (1%) and biogenic substance (0.5%).

Seventy-one articles sampled and analyzed surface water such as streams, rivers, lakes, reservoirs, and creeks. The factors affecting the quality of surface water as identified from these studies are pathogens (26.8%), industrial wastes (23.9%), metals and naturally occurring substances (22.5%), pharmaceuticals (12.7%), agricultural wastes (7.0%), wildfire (5.4%), biogenic (1.4%). Table 6 below shows these factors and examples from the study.

Eighty-eight articles sampled and analyzed ground water which permeates below the soil and stored in the tiny spaces (pores) between rocks and particles of soil. The factors affecting the quality of ground water from the articles reviewed are industrial wastes (32.9%), metals and naturally occurring substances (25%), pathogens (25%), pharmaceuticals (7.9%), agricultural wastes (7.9%), and biogenic (1.1%). Table 7 below shows these factors and examples of the contaminants.

Twenty-five articles sampled and analyzed water at the water treatment plants before water treatment processes occurred. The leading factor identified was pathogens (28 %) followed by pharmaceuticals (24%), industrial wastes (24%), metals and naturally occurring substances(12%), agricultural wastes (4%), wildfire (4%) and natural disaster (4%). Table 8 below shows the factors affecting the quality of water at the water treatment plants.

One study sampled water in the water distribution network. It assessed the concentrations of halide compounds in the distribution system.

Seventy-one articles sampled and analyzed tap water. The most observed factor affecting the quality of tap water was pathogens (42.3%) followed by metals and naturally occurring substances (31%), industrial products (12.7%), pharmaceuticals (8.5%), and agricultural wastes (5.6%). Table 10 below shows the factors affecting tap water and examples.

Five studies sampled and analyzed bottled water. The factors affecting the quality of bottled water are industrial wastes (40%), metals and naturally occurring substances (40%) and pathogens (20%). Table 11 below shows the factors affecting the quality of bottled water.

4. Discussion

This systematic review highlights some of the factors that affect the quality of drinking water in the United States by reviewing 201 articles published between 2010-2020. We observed that the highest number of articles were from Pennsylvania State and northeast region of the United States. In 2017, Pennsylvania state faced enormous water crisis from lead-contaminated drinking water in Pittsburgh, to sick and dying fish in the Susquehanna, to rainwater runoff contaminated with industrial pollutants in Delaware. The rivers and streams are stressed with many showing signs of ecological decline ²⁵. Similarly, the whole of the northeast region had its share of water crisis as well during this period. Some of these problems include the presence of lead, iron, manganese, and other metals that give source and tap water in some counties in this region its characteristic smell/odor, color, and hardness. The increasing industrial activities and ageing water distribution pipes have been implicated to be responsible for the challenges in water supply and contamination ²⁶. Therefore, it is plausible that research and publications on water issues are likely to emanate from region with serious water challenges compared with those with moderate to mild problems.

Majority of the articles sampled and analyzed water from urban settings. Urban areas are hub for commercial activities and the United States Census Bureau states that 80.7% of the U.S. population resides in the urban areas ²⁷. Also, public water distribution system that supply drinking water to 90% of Americans are also situated there. Urban waters usually carry-on substantial pollution from industrial effluents, commercial wastewater and polluted stormwater runoff which have negative impact on the ecosystems and water quality ²⁸. However, the unpleasant occurrence of water pollution in an urban area is usually matched with adequate attention and response by the media, civil society, researchers, and government agencies. These may account for the high percentage of water sampling from urban areas among the articles reviewed.

The methodology used in the articles reviewed varied in sampling, study design and analysis because of the heterogeneity of these articles and focus on different factors that affect quality of water. However, the most common study design observed was inductively coupled plasma mass spectrometry. This technique atomizes water sample easily, highly sensitive in detecting metals & non-metals at low concentrations and simultaneously detect multiple trace elements ²⁹. It can quickly differentiate isotopes of the same element and this characteristic makes it a procedure of choice for identifying undesirable elements in drinking water.

Furthermore, the most common contaminant identified in this study was chemical waste, followed by pathogens. The discharge of chemical wastes into the environment and water bodies is one of the aftermaths of industrialization. Some of these chemical wastes, unfortunately, often find their ways to the tap and consumers’ table. Evans et al., observed that the cumulative risk analysis of contaminant occurrence in United States drinking water for the period of 2010-2017 indicated that over 100,000 lifetime cancer cases could be due to carcinogenic chemicals in tap water. Most of this risk is due to the presence of arsenic, disinfection byproducts and radioactive contaminants ³⁰. Similarly, Andrew and colleagues observed that chemicals like per- and polyfluoroalkyl substances are nearly ubiquitous in surface water, the predominant source of drinking water for the U.S. population. It was estimated that 18–80 million people in the U.S. receive tap water with 10 ng/L or greater concentration of perfluorooctanoic acid and perfluoro-octane sulfonate combined, and over 200 million people likely receive water with a PFOA and PFOS concentration at or above 1 ng/L ³¹.

Surface water is any body of water found on the earth’s surface, including the saltwater in the ocean and the freshwater in rivers, streams, and lakes. It is highly susceptible to pollution because it runs on earth’s surface and easily contaminated by stormwater run-off, human and animal excreta which introduce micro-organisms such as Escherichia Coli and other particulate matter into it. This study identified the following as the factors affecting the quality surface water; pathogens, industrial wastes, metals and naturally occurring substances, pharmaceuticals, agricultural wastes, wildfire, and biogenic substance. Industrial waste is one of the major factors identified that affect the quality surface water. This is in tandem with James et al observation during a multi-agency study of organic and inorganic chemicals in urban stormwater from 50 runoff events at 21 sites across the United States. It was reported that stormwater transports substantial mixtures of polycyclic aromatic hydrocarbons, bioactive contaminants (pesticides and pharmaceuticals), and other organic chemicals known or suspected to pose threat to surface water quality and safety of the environmental ³².

Similarly, per- and poly-fluoroalkyl substances have been recognized as surface water contaminants of emerging concerns by the United States Environmental Protection Agency (USEPA) due to their environmental impact. They have been observed to be several folds higher than the US EPA health advisory level of 70 ng/L for lifetime exposure from drinking water. Direct discharge and atmospheric deposition were identified as primary sources of PFAS in surface water and cryosphere respectively ³³. Agricultural activities such as fertilizers, pesticides and fungicides applications to a farmland also cause contamination of contiguous surface water. Glinski et al., in a study titled, “Analysis of pesticides in surface water, stemflow, and throughfall in an agricultural area in South Georgia” observed that the most frequently detected pesticide in surface water and stemflow samples was met alachlor (0.09–10.5μg/L) and the most detected pesticide in throughfall samples was biphenyl 0.02–0.07µg/L ³⁴. The presence of these substances makes surface water unfit for swimming, fishing, and drinking purposes due to the negative health effects on human beings.

Groundwater is the part of rainfall that seeps down through the soil until it reaches rock material that is saturated with water. It is stored in the spaces between rock particles. It is very important because it provides 25% of the fresh water used in the United States and many rural communities depend on it as their source of drinking water ³⁵. It becomes polluted when contaminants leached from landfills and septic systems into aquifers making it unsafe for human consumption. This study identified industrial wastes, metals and naturally occurring substances, pathogens, pharmaceuticals, agricultural wastes, and biogenic substances as factors affecting the quality of groundwater.

The increasing contamination of ground water by metals and naturally occurring substances, such as arsenic, manganese, and hexavalent chromium was observed to be widespread among the articles reviewed. This is in consonance with McMahon et al observation in a study titled, “Elevated manganese concentrations in United States groundwater, role of land surface–soil–aquifer connections”. They reported that an estimated 2.6 million people consume groundwater with elevated manganese concentrations, the highest densities of which occur near rivers and in areas with organic carbon rich soil ³⁶. Also, Coyte et al., in a study on groundwater titled, “Occurrence and distribution of hexavalent chromium in groundwater from North Carolina, USA”, identified several areas in the Piedmont region where chromium Cr (VI) concentrations in groundwater was above health guidelines which posed high human health risks to large populations in the eastern united states ³⁷. Furthermore, the first large-scale, systematic assessment of hormone and pharmaceutical occurrence in groundwater used for drinking across the United States revealed that at least one compound was detected at 5.9% of 844 sites representing the resource used for public supply across the entirety of 15 Principal Aquifers and detections were most common in shallow wells ³⁸.

Water treatment plants employ processes and modern techniques to treat wastewater until it is clean and safe again for human use. The United States has over 16,000 wastewater treatment plants that treat wastewater that is collected from homes, businesses, and industries. This study identified the following factors that affect the quality of water in treatment plants; pathogens, pharmaceuticals, industrial wastes, metals and naturally occurring substances, agricultural wastes, wildfire, and natural disaster. King et al, obtained drinking water at 25 treatment plants across the United States and screened for nine pathogens. They observed that pathogens are widespread in source waters, but that treatment is generally effective in reducing them to below detection limits. The one exception is the mycobacteria, which were commonly detected in treated water, even when not detected in source waters ³⁹. Natural disaster is another factor that affects the quality of water depending on its magnitude. The catastrophic destructions that trail events such as hurricane often affect water infrastructure making clean water a serious challenge for the affected communities.

Water treatment plants are very important to reducing human exposure to contaminants and outbreak of diseases. The prevalence of waterborne diseases would be reduced to the barest minimum if water emanating from the treatment plants conform to US EPA regulatory requirements. The Safe Drinking Water Act sets maximum contaminant levels or enforceable standards for some pathogens, which are published in the Code of Federal Regulations (CFR) under Title 40 CFR §141 subpart ⁴⁰.

Water distribution system infrastructure comprises the pipes, pumps, valves, storage tanks, reservoirs, meters, fittings, and other components that connect treatment plants or well supplies to consumers’ taps. This system is made up of 2.2 million miles of underground pipes called water mains, that deliver safe, reliable water to millions of people.

In this study, only one article sampled water in the water distribution network. It assessed the concentrations of halide compounds in the distribution system. Total organic chlorine (TOCl), bromine (TOBr) and iodine (TOI) species and collectively total organic halide (TOX) concentrations were quantified quarterly at 11 US drinking water treatment plants (WTPs) and distribution systems. It observed increase in TOCl as the intake of dissolved organic chlorine increased in some plants ⁴¹.

The challenges with the distribution systems are the ageing infrastructure and breakage along the distribution pipes. In 2020, the average age of water pipes in the U.S. was 45 years old -- an increase in average age from 25 years old in 1970. Each year, 250,000 to 300,000 main breaks occur in the U.S., disrupting supply and risking contamination of drinking water ⁴².

In this study, the most common factor affecting the quality of tap water was pathogens followed by metals and naturally occurring substances, industrial products, pharmaceuticals, and agricultural wastes. The drinking water is regulated by State and federal laws that stipulate maximum contaminant levels and treatment requirements for some pollutants and naturally occurring constituents. Tap water is safe for drinking in most parts of the United State. However, there is growing distrust among citizens to the extent that some prefer bottled to tap water. Rosinger et al., in a nationally representative U.S. trends analysis of in-home tap water avoidance between 2007 and 2016 observed that younger children, Hispanic, non-Hispanic black, and those from low socioeconomic status backgrounds had consistently higher probability of avoiding tap water over time. Children who avoided tap water had 92% higher prevalence of drinking bottled water. In 2015–2016, 78% of non-Hispanic black children who avoided tap water drank bottled water on a given day ⁴³. Similarly, Leila et al in a water consumption survey with 1,171 participants, observed that 48% of the respondents reported drinking tap water daily compared with 58% who reported drinking bottled water daily. The reason they cited for not drinking tap water was perceived health risks ⁴⁴.

Over the last decade, annual bottled water consumption increased by 40 percent, reaching a total of almost 44 gallons per person in 2019. This increase may be due to the notion that bottled water is safer than tap water especially among the Hispanic and Black households ⁴⁵. Bottled water sometimes contains contaminants that are unsafe for human consumption. This study identified industrial wastes, metals and naturally occurring substances and pathogens as some of the factors that affect the quality of bottled water. This is similar with Chowdhury et al findings in a study titled, “Spectrochemical Analysis of Bottled and Tap Water from Selected Counties of Middle Tennessee, USA. A total of 37 elements were observed in tap and bottled water samples from six counties of Middle Tennessee (USA) by Inductively Coupled Plasma Optical Emission Spectrometry ⁴⁶.

Chow et al., in a study titled, “detection of ultrashort-chain and other per- and polyfluoroalkyl substances (PFAS) in U.S. bottled water”, investigated the occurrence of PFAS and related factors in 101 uniquely labelled bottled water products for sale in the United States. Ultrashort-chain measured for the first time in bottled water, accounted for the greatest individual fraction of detected PFAS mass (42%) and was found almost exclusively in products labeled as Spring water ⁴⁷.

5. Strength and Limitation

This review was based on a protocol that was created beforehand and outlined the methodology used throughout. Also, a comprehensive search strategy helped to capture large numbers of studies. Blinding during selection and screening of articles helped to reduce bias. This review was limited to studies conducted only in the United States, so it may not be generalizable. However, we made efforts to search relevant databases and retrieved 12,722 articles and reviewed 201 articles in detail Secondly, we did not cover gray literature. Since gray literatures are not published in peer-reviewed journals, we may not have captured all the available literatures on this subject. Third, it was also limited to a narrative analysis and did not include a meta-analysis due to high sample, experimental and statistical plurality.

6. Recommendation and Conclusion

This systematic review highlighted some of the factors that affect the quality of drinking water in the last decade in the United States. It is evident from these literatures that the factors include wastes from industrial activities, pathogenic micro-organisms especially from fecal contamination of water, agricultural practices, naturally occurring substances, pharmaceutical substances, and natural disasters. The consequences of these factors on human health and ecosystems can be reduced to the barest minimum by taking specific action to address them. We therefore want to make the following recommendations

a) Unites States Environmental Protection Agency (US EPA) should be given more human and material resources to enforce the Safe Drinking Water Act (SDWA) and synergize with states in enforcing their own drinking water standards

b) Regulation of discharge of industrial effluents into the environment or water bodies

c) Routine testing of private and public water supplies for various contaminants on a periodic basis to ascertain changes in contaminant levels.

d) Communities and individuals should take more active roles in protecting drinking water sources from pollution.

e) Refurbishing ageing water infrastructure

In conclusion, drinking water sources are contaminated by natural substances in the environment and human activities. Such contaminated water is not only injurious to human health and other living organisms, but it also kills. In fact, globally it caused 1.8 million deaths in 2015 and makes about 1 billion people sick every year ⁴⁸. The burden of waterborne diseases in the United States show that every year, waterborne diseases cause 7.15 million illnesses and 6,630 deaths and cost our healthcare system more than $3.3 billion ⁴⁹. Therefore, to mitigate the negative impact of contaminated drinking water on humans, there must be concerted effort to implement appropriate water policies, protect water sources and invest in water infrastructure for an enduring and sustainable future.

Conflicts of Interest

The authors declare no conflicts of interest exist

Authors’ Contributions

KO conceived and designed the study under the supervision of SK. LC is a University Librarian who designed the search strategy and extracted the articles from the databases. KO and PJ independently screened and assessed the articles for eligibility. KO and PJ extracted the results from the excel sheet. KO drafted the manuscript. All authors critically reviewed the manuscript and approved the final version.

Acknowledgements

The authors would like to thank everyone who played one role or the other during this review. We are grateful to you all.

References