Assessment of quality and health risks in drinking water sources in Aba, Nigeria Open Access

As populations in developing countries continue to increase, the pressure on water resources also increases, leading to significant problems in maintaining water quality and access to safe drinking water. An increase in the world's rural-to-urban migration is projected to be influenced by developing countries, such as India, China, and Nigeria. This movement is expected to contribute to a 35% increase in the global urban population by 2050 (UN DESA 2018). Therefore, there is a need for these countries to commensurately improve infrastructure development to keep up with the demands of the urban population. However, this is seemingly not the case, especially for Nigeria, which is faced with serial infrastructural deficits in its urban implementation. For instance, since the return of civilian administration in 1999, piped-treated water in most buildings and living spaces has been regarded as luxury. Nigeria has the lowest proportion of urban dwellers with access to 11% of piped water within the sub-Saharan African region (UNICEF 2019). Currently, private water is the most practiced supply system from vendors and shallow water tables in both urban and rural areas (Edet et al. 2011). Presently, half of the Nigerian population lives in urban areas; however, it has been documented that only 23 million urban dwellers have access to piped water via water corporations, while 69 million do not (USAID 2023), raising the question of the safety of drinking water sources in the country.

Several studies have shown that unregulated urban practices harm the chemical and biological qualities of natural drinking water sources (Barrett et al. 2000; Lapworth et al. 2017a; Ijioma 2021b). Some examples of such practices include the use of leaky septage drains and on-site sanitation facilities, manure stockpiles from animal dung (Egboka et al. 1989), stormwater runoff containing feces of humans and domesticated animals, as well as biological contamination from open dumpsites (Lapworth et al. 2017b), and poor municipal and industrial waste (effluent and solid) management (Ijioma 2021b). These practices compromise the chemical and bacteriological qualities of water sources and jeopardize public health.

Different criteria have been employed when assessing the quality of drinking water sources. These criteria consider the physical, chemical, radiological, and biological properties of the water. Chemical contamination in drinking water is mostly geogenic in nature in many developing countries; however, biological health risks are reported to be the most potent cause of water-related health problems in urban areas (Wright et al. 2004; Banda et al. 2014; Sorensen et al. 2015; Gwimbi et al. 2019; Nzung'aSila 2019). Notably, diarrhea, which causes over 800,000 deaths annually (CDC 2015; Carvajal-Vélez et al. 2016), and cholera outbreaks have recently occurred in various parts of Nigeria (NCDC 2021; reliefweb 2021). It is important to note that most microbial contamination in the environment is due to anthropogenic activities linked to poor sanitation.

To safeguard the environment and promote sustainable development, governments and international agencies have developed and/or adopted policy initiatives, international treaties, guidelines, and regulations as tools to actualize them (Ogunkan 2022). The most reliable international environmental instruments used for drinking water safety regulations include UN Sustainable Development Goal 6 (SDG 6), Guidelines for Drinking Water Quality and Water Safety Plans (WSPs) by the World Health Organization (WHO), and the Stockholm Water Declaration (1991). Nigeria, as a party to various UN treaties and initiatives on the environment, adopted these tools to frame some of her national policies, guidelines, and action plans that regulate, ensure equitable access, and protect the water sources to meet the needs of the people.

Despite having several environmental policy instruments in place that protect the natural ecosystem, poor quality and water insecurity issues still prevail in different urban areas of Nigeria. For instance, using a case of a developing urban area such as Aba, many scholars have conducted studies within the study area to ascertain the quality of drinking water sources. These investigations include the quality assessment of natural water sources (Adindu Igbokwe & Lebe 2012; Akakuru et al. 2017; Agharanya & Dim 2018; Nnorom et al. 2019), identification of contamination sources (Ijioma 2021a; Okeke et al. 2023), and risk assessment and evaluation of secondary drinking water sources using certain quality indicators and indices (Aroh et al. 2010; Mgbakor et al. 2011; Ajala et al. 2020). It is noteworthy that natural drinking water (surface and groundwater) sources in the area are connected (Agharanya & Dim 2018; Nnorom et al. 2019). In as much as the outcomes of these studies provided valuable baseline quality assessment for drinking water sources, however, they do not provide a holistic approach to appraise health risks and integrate policies that protect drinking water sources, given the poor state of water supply in the area. In this study, a holistic dimension was employed (encompassing both laboratory and empirical methods) and guided by the water safety plan (WSP) framework to evaluate health risks in natural and secondary drinking water sources in Aba, Nigeria. To the best of our knowledge, this is the first time that this approach has been employed for risk assessment, considering the dysfunctional state of waterwork schemes. Furthermore, this study reinforces the need to review environmental laws and policy integration and provide additional data necessary for the advanced modeling of risks associated with drinking water sources. Specifically, this study aimed to (a) identify the main water sources from which drinking water is derived and determine the environmental hazards associated with these sources; (b) measure and compare human health risks (i.e., chemical and biological) in selected drinking water sources; and (c) review gaps in environmental laws of Nigeria as tools for protecting water resources in the country.

Aba has an estimated population of over 1 million people and is the fourth most densely populated urban area in Nigeria. There are two main climate seasons throughout the year: rainy (April–October) and dry (November–March). The area has typical rainforest vegetation and receives a high volume of rainfall (2,540 mm/annum), which gives it an ultra-humid climate. The geology of the area is basically coastal plain sand derived from the quaternary Benin Formation (Onyeagocha 1980; Reijers 2011), and the geological material serves as an excellent aquifer. Relief analysis of Aba revealed that it was predominantly low-lying flat land. The area is drained by the perennial Aba River, a tributary of the Imo River system that flows into the Atlantic Ocean. The analysis of the classified land-use map between 1986 and 2020 revealed rapid growth trends in the built-up class. The built-up class is of mixed residential and commercial use and currently covers approximately 37% of the area (Ijioma 2021a). There are currently three state-owned dysfunctional waterwork schemes, and there is no central municipal sewer system in the area. This implies that household, industrial, and municipal effluents infiltrate underground or drain into the river.

The WSP framework was used as an analytical tool to evaluate the safety of drinking water sources even though there is no functional water scheme that supplies water to the area. The WSP approach follows holistic drinking water risk assessment and management from the catchment through treatment and distribution to the point of consumption (Bartram et al. 2009; WHO 2023). The WSP was used to evaluate the risks in drinking water sources in four steps, spanning from the catchment to the point of consumption. First, system assessment identifies potential hazards in drinking water sources and potentially affected people. This was achieved through empirical surveys and observed land-use practices that influence drinking water quality. The second phase is the quality monitoring stage, which assesses risks by quantifying selected quality indicators (chemical and biological) in different drinking water samples. The results of the evaluation were compared with the recommended standards defined by the WHO and Nigerian Industrial Standards (NIS) for drinking water quality. The third phase is the management and communication stage, which requires that the identified risks are controlled to ensure that public health is protected. This stage entails the identification of existing water-related policies and environmental governance structures that prevent the identified hazards in different drinking water sources in the country. Finally, the feedback stage summarized the main findings and evaluated and recommended action plans that put barriers to the identified hazards and improve the safety of drinking water sources. This cyclic process results in a continuous improvement that ensures drinking water safety from the catchment level to the point of consumption.

Surveys were conducted among households and other selected stakeholders using questionnaires and semi-structured interviews to fulfill the set of objectives for the system assessment of the WSP framework (see the attached sample of the survey questionnaire as a supplementary document). A multistage sampling technique was adopted in selecting respondents to obtain a general perception of the water situation in the area. Questionnaires were distributed to 120 randomly selected households drawn from 10 residential blocks in Aba (see Figure 1(c) for the spatial distribution of the respondents) using face-to-face interviews. The first part of the questionnaire asked the respondents about the origin of their drinking water sources and the type of water facility from which the water came. The respondents were asked about their awareness of the quality of drinking water sources. They were asked to rank some identified urban practices that contaminated the water sources.

For quality awareness, aesthetic properties and consideration of pretreatment before drinking water were used as perceived criteria for quality. Semi-structured interviews were used to identify follow-up themes arising after the questionnaire exercise from 10 experts. Respondents were drawn from manufacturing industries (4), academia (3), and government agencies (3). Purposive and snowballing techniques were employed to select the next respondent for each interest group, and requests for referrals ceased at the point of data saturation. Based on the thematic issues guiding the questionnaire, simple descriptive statistical and GIS-based illustrations depicting important land use-derived hotspots were created to summarize the main findings of the questionnaires.

To assess and quantify the risks, drinking water samples from different sources were analyzed. Representative water samples were taken following standard operating procedures for different catchment-level samplings. These included samples from (a) groundwater, (b) Aba River water, and (c) rainwater. Groundwater samples were randomly collected from 60 points. Groundwater samples were taken via the bypass outlet between the submersible motor (SUMO) pump and the storage tank. Purging the tube wells was not necessary before sampling because all the selected wells were production wells and were frequently used. The samples of the Aba River were collected at four different points: the stream head and three other points downstream around dense residential areas. Rainwater samples were obtained using a clean funnel to direct rainwater into the container until a sufficient volume of rain (500 ml) was collected in both peri-urban and dense residential areas. The most common method of rainwater harvesting for domestic use in Aba is rooftop interception. Samples from secondary drinking water sources (n = 19) manufactured in Aba were randomly collected. These samples include treated piped water, water-in-sachet, also known as ‘pure water’, PET or polyethylene bottled water, and beverage drinks (alcohol and non-alcohol). Samples from secondary drinking sources were only considered for bacteriological investigations. For the different methods of analysis, ionized distilled water was used as a control following the standard operating procedures for each parameter monitored in the samples. The geographical coordinates of the identified poor land-use practices that were observed to have the potential to contaminate drinking water sources were collected and used to develop a potential contamination source map for drinking water sources in the area.

Fifteen physicochemical and chemical drinking water quality indicators were assessed for general chemistry, based on the influence of land use on natural water sources. These indicators include pH, TDS (for the physicochemical), Ca, Mg, Na, K, Cl, SO₄, HCO₃, and NO₃ (for major cations and anions), and some trace heavy metals such as Cd, Pb, Cr, Fe, and Mn (trace metals or potential toxic elements) were considered. Table 1 lists the different methods that describe the standard operating procedures for analyzing each quality indicator in water samples based on the American Society for Testing and Materials (ASTM) and the Animal and Plant Health Agency (APHA) protocols.

Biological risk evaluation in drinking water sources was assessed based on the incidence of indicator organisms. This assessment method utilizes a membrane filtration technique. Thirty-six samples in triplicate from different drinking water sources (natural and secondary) were analyzed following the ISO 7704:1985 protocol. Commercially prepared ready-to-use Coliforms Chromogenic Agar (CCA) media manufactured by VWR Chemical Germany were used to analyze different drinking water sources. This medium selectively isolated colonies of E. coli and other coliform bacteria from the samples. The substrates in the agar medium cleaved to the β-d-galactosidase enzyme in coliform bacteria and the β-d-glucuronidase enzyme in E. coli, giving the colonies salmon-red and dark-violet coloration, respectively (VWR Chemical 2019). The selected drinking samples were appropriately diluted and filtered through sterile 45-μm membrane filters under vacuum. The inoculated filter paper for each sample was placed on top of an agar medium Petri dish and incubated at 35 ± 1 °C for 44 ± 4 h. The microbial count per milliliter in each sample was determined by multiplying the inverse dilution factors with the average number of colonies present in each membrane.

The human health risk assessment of drinking water sources was estimated using the HQ/HI values, where HQ/HI < 1 denotes minimal or non-existent risk in the drinking water source. However, when HI < 0.1, it connotes negligible risk; HI ≥ 0.1, but <1 connotes low risk; HI ≥ 1 but <4, medium risk; and HI ≥ 4, high risk (USEPA 1999; Paustenbach 2002).

The evaluation of bacteriological risks in drinking water sources was based on the average number of incidences of total coliform and E. coli bacterial colony-forming units in the samples and comparing them for the various sources. A case of no incidence or zero incidence of E. coli and/or total coliforms in the sample means that the water source is safe and there is no risk associated (WHO 2011). Table 2 summarizes the risk classes for drinking water sources.

The respondents were representatives of households in various parts of Aba. The breakdown of participants showed that 54% were male and 46% were female. The participants were educated (95% had completed at least primary education) and the average household size was 4.5 people. The distribution of accommodation unit types among the respondents can be described as follows: multi-room apartments (49%), single-room units (42%), and whole buildings (9%). Most respondents who lived in informal residential areas used single-room accommodation. Urban implementation in these areas is poor. Most households do not have access to water supplies for domestic use within their compounds. Here, households fetch water and store it in containers from neighboring compounds where there are boreholes, which come at a cost. In rare cases when the water supply is free, the availability is not frequent and guaranteed.

Three freshwater sources (groundwater, water from the Aba River, and rainwater) were identified as potential sources of domestic water. However, the results of the surveys revealed that all respondents (100%) derived drinking water from groundwater. This means that at both the catchment level (from natural sources) and/or secondary products, such as water-in-sachets or beverage drinks, the origin of water for making the product was derived from groundwater (tube wells). The order of reliability in the context of access to water is groundwater > surface water from the Aba River > rainwater. Notably, despite the perennial nature of the Aba River, this source is less dependable for domestic use, because it receives both industrial effluents and urban storm runoff. Therefore, the river was perceived to be highly contaminated. Rainwater is a seasonal source of freshwater. Rainwater is sufficiently available during rainy months (March to October).

Although the existing water schemes in the area were all dysfunctional, the drinking water source for all respondents suggested that they belong to the improved category according to the Joint Monitoring Programme (JMP) classification of WHO/UNICEF for water facilities relating to water supply, sanitation, and hygiene. The identified drinking water sources included tube wells/boreholes, secondary/treated sources, and treated piped water, representing 50, 48, and 2%, respectively. The treated pipe water was obtained from standalone tap outlets at one of the beer brewery plants in the area. The breakdown of the secondary drinking sources comprised 45% packaged water-in-sachets and 3% representing bottled water either in polyethylene terephthalate (PET) or polyethylene (PE) containers. Packaged water-in-sachets are the most commonly used secondary drinking water source. This observation is popular and has been widely reported in studies conducted in developing countries (Hawkins 2017; Morinville 2017). Bottled water is more expensive than water in the sachets. It is the most consumed among the rich and is believed to be of better quality. However, there are still doubts regarding the quality of the bottled products produced by unlicensed bottled water manufacturers. Cases like this make some bottled water be treated in the same way as ‘sachet water’.

The tube wells/boreholes are the main source of domestic water supply, but these wells are indiscriminately drilled in residential properties without permits. In shanty neighborhoods, where the services of biosolid sludge evacuators are rarely used, sludges are buried in backyards, and many sludge evacuation agents do not have a standard treatment facility, so they discharge biosolids downstream of the Aba River. These types of practices have been reported in different developing urban areas of sub-Saharan Africa (Cissé Faye et al. 2004; UN-Habitat 2008; Banda et al. 2014; Lapworth et al. 2017a; Diaw et al. 2019; Akakuru et al. 2021). In addition, the quality of the Aba River is heavily impacted by poor urban practices such as direct discharge of industrial effluents, household waste especially black water (i.e., mixture of urine and open defecation), rearing of animals, and slaughtering activities near the riverbanks, as well as channeling abattoir effluents into the river without treatment through the open canals. These land-use activities are not peculiar to the study area but are also widely reported in many other developing urban areas (Barrett et al. 2000; Chukwu et al. 2011). Another source of contamination in both surface and groundwater is the poor management of municipal solid waste in the area (see Figure 3(c)). Most often, dumpsites and overflowing collection bins are rampant on major streets. The landfills for unsorted municipal waste were derived from borrow-pits and erosion sites. Occasionally, these landfills are located near residential buildings. The composition of municipal refuse waste ranges from kitchen waste to medical waste (e.g., used swabs, fresh body parts, aborted fetuses, animal carcasses, etc.), batteries, electric and electronic waste, damaged household items, etc. This type of waste management practice was crude and highly rated by the respondents in the survey.

The leachates generated from the waste in the dumpsite seep through the vadose zone, reaching the groundwater and worsening its quality. Other poor practices include draining wastewater from fishponds into recharge wells (Figure 3(f)) and the use of untreated stormwater from waterlogs as circulating fluid during borehole drilling. Rainwater is an important natural source of drinking water if properly harvested. However, the supply of rainwater is not reliable because of climate change, and rain is only available during the rainy season. Several studies have reported that the physicochemical and microbial qualities of rainwater collected from rooftops are not safe (Meera & Mansoor Ahammed 2006; Ahmed et al. 2011; Hamilton et al. 2019). This may be due to contamination from droppings from birds, insects, mammals, and reptiles (Ahmed et al. 2011), or sometimes, dissolved or particulate solids from roofing sheets (e.g., asbestos, iron, and other corroded metal materials). These are sources of hazards that degrade the biological, chemical, and aesthetic value of drinking water sources in the area.

As shown in Figure 4, the median values of major cations and trace metals, such as Ca, Mg, Cd, and Fe, were higher in the Aba River than those measured in groundwater. This observation can be attributed to the impact of direct effluent discharge by chemical industries into the Aba River and direct storm runoff through the surface canal into the Aba River. However, as expected, the groundwater samples had higher concentrations of major ions than the Aba River and rainwater samples. This is consistent with the TDS, HCO₃, Cl, NO₃, SO₄, Na, and K values in the groundwater. The increased TDS spread in the groundwater can be positively correlated with an increase in the major ions of samples, especially in dense residential areas (Ijioma 2021a). This observation supported some responses from household surveys of people living in dense residential areas who reported that groundwater in their area has objectionable tastes. Some man-made sources of the major ions in the groundwater were linked to the use of septage, dumpsite leachates, and intensified concrete construction activities (Ijioma 2021a). It is important to mention that the high amount of rainfall received in the area might be responsible for the low mineralization of both major ions and trace metals in the water sources, despite the influence of rapid population growth and poor urban land-use practices observed over the years in the area.

Not all the chemical quality indicators measured in water samples have adverse health implications. The chemical risks in natural water sources (groundwater, rainwater, and surface water) were evaluated based on the presence and concentrations of potentially toxic elements measured in the water samples. The trace metals considered included Cd, Cr, Fe, Pb, and Mn. These potentially toxic elements have known health implications when they are present in drinking water above their MAC values.

The health risks associated with these indicators include kidney damage, bone degradation, cardiovascular diseases, and an increased risk of cancer when concentrations of Cd are above 0.003 mg/l in drinking water, and carcinogenic potency for Cr when concentrations are above 0.05 mg/l. Again, impaired neurological developmental effect, impaired renal function, hypertension, and reproductive issues especially in fetuses, infants, and children because of Pb poisoning containing more than 0.01 mg/l, and neurological, and when Mn is present in intolerable concentration leads to loss of cognitive ability for concentrations more than 0.08 mg/l (WHO 2022). Table 3 summarizes the HQ and HI for the Aba River and groundwater samples taken from both urban (u) and peri-urban areas. The HQ/HI estimations suggest that there are low-risk concerns since the values of the HI are ≥0.1, but <1 for both samples of water from the Aba River and groundwater. The HQ/HI results corroborate the findings of Nnorom et al. (2019) in their assessment of the water sources in the region. Again, the HQ/HI estimations suggested increased risks in children compared with adults, and the risks heightened by the sources based on the array: Aba River < groundwater (peri-urban) < groundwater (urban). This is due to the impact of rapid urbanization and unregulated anthropogenic activities in dense residential areas (Ijioma 2021b).

The incidence of indicator organisms in these natural drinking water sources suggests high health risks if people drink directly from these sources, without prior treatment. It can be observed that biological contamination in the Aba River samples was greater than that detected in groundwater. This can be explained by the lack of physical barriers or weakly enforced policies for surface water bodies, such as the Aba River, which makes it more vulnerable to contamination. This is based on the current physical state and results of bacteriological analysis. For the secondary drinking sources, 1.0 × 10³ and 1.5 × 10² cfu/100 ml coliform bacteria were detected in beverage and packaged water products, respectively. The WHO and Nigeria Industrial Standards recommend safe drinking water MAC values for total coliforms and E. coli of zero. This value was exceeded, rendering the samples unsafe for drinking. Production licensing approval for packaged water-in-sachet products is required by the National Agency for Food and Drug Administration and Control (NAFDAC), yet quality control enforcement for these products is not guaranteed. Several studies have reported evidence of a bacteriological compromise in the quality of packaged water-in-sachets in various parts of Nigeria (Malik et al. 2014; Ajala et al. 2020; Ihesie et al. 2021; Udoh et al. 2021). It has also been found that the use of non-sterile packaging materials (Omalu et al. 2010), unhygienic handling conditions in the distribution line, and poor and long storage (Akinde et al. 2011) are some of the factors responsible for the bacteriological contamination of secondary drinking products. The treated piped water samples showed zero incidence of the indicator organisms, indicating that the source was safe according to the WHO criteria for E. coli and total coliform indicators.

From colonial times to this day, there are many legal and institutional instruments in the form of laws, acts, degrees, policies, and regulations designed to protect the environment from human interference in Nigeria (Akpabio 2012). With the growing population in urban areas, these instruments help regulate some urban practices identified as hazards to avert impending health concerns. According to Odey (2023), some of these instruments before 1989 focused mostly on sanitation rather than environmental protection. However, some environmental and institutional instruments have been promulgated to correct and protect various aspects of the environment. Table 5 summarizes the recent environmental acts, laws, policies, and regulations that protect water resources in Nigeria. The Federal Ministry of Water Resources (FMWR) is the leading authority in formulating policies, plans, and programs to ensure the sustainable use of water resources (FMWR 2016). It collaborates with other relevant ministries, agencies, and stakeholders in the water sector to ensure effective coordination and implementation of initiatives to safeguard water bodies in Nigeria (FGN 2004). Other federal agencies working under or with the FMWR to protect natural water bodies in Nigeria include the National Water Resources Institute (NWRI), Federal Ministry of Environment (FME), Federal Ministry of Agriculture and Food Security (FMAFS), National Environmental Standards and Regulations Enforcement Agency (NESREA), and National Oil Spill Detection and Response Agency (NOSDRA). However, NESREA is under the FME and is responsible for protecting water resources. At the state and local levels, the implication and supply of safe drinking water are the tasks of institutions such as the NAFDAC and State Water, Sanitation, and Regulatory Agencies. NAFDAC is responsible for licensing production and setting standards for packaged water and other secondary drinking water products. Despite multiple environmental instruments and implementing agencies, the pollution of natural water courses remains evident in many parts of the country. One of the main challenges faced by existing instruments is the selective justice system, which arises from weak policy implementation due to corruption.

We also agree with the assertions of Odey (2023) that other factors, including overlapping roles among enforcement agencies, lack of modern technologies for environmental monitoring, limited funds for agencies to prosecute offenders, and lenient penalties for violators, all hinder the effectiveness of instruments and institutions in protecting drinking water sources.

According to Adeoti (2007), the inability of states and local government authorities in Nigeria to tailor local water policy guidelines that suit their peculiarities may be one of the reasons why the enforcement of drinking water safety cannot be sufficiently guaranteed.

In this study, groundwater, surface water (Aba River), and rainwater were identified as the main natural sources of drinking water in Aba. Presently, groundwater is the primary source of drinking water, from which all secondary drinking products are derived. The overall physical properties of the groundwater look good, and this is why most people believe that the water is ‘pure’ and therefore do not pretreat the water before drinking. The geology and lithology of the area confer the aquifer a semi-confined status, which translates to physical protection and a good baseline water quality for the groundwater, as observed.

The results of the analyses of the water samples suggest that there are currently low-risk concerns for the selected potential toxic indicators for different water sources. Although this study did not investigate health issues to implicate some of the identified urban practices mentioned, the HQ/HI estimations in the different water sources suggest that drinking water quality is deteriorating, especially for groundwater in areas with intensive urban activities. On the other hand, the incidence of bacteriological contamination observed in water samples from the Aba River and the sachet water products also suggests that quality regulation of these products should be taken seriously to avert impending public health crises.

While we acknowledge a plethora of laws and policies that should protect drinking water sources in Nigeria, the benefits of these instruments can only be actualized when there is a political will to strengthen responsible institutions and local authorities who enforce and implement the programs. The problem of ‘strong man syndrome’, which describes a situation where certain individuals are more powerful than institutions, results in selective justice. This should be discouraged and enforcing institutions enabled to ensure no one is above the law. Environmental agencies must raise awareness and educate people about the implications of some poor environmental practices that harm the quality of water sources and hold offenders accountable for their actions. Therefore, environmental instruments must be reviewed frequently, so that commensurate penalties deter offenders and prevent future occurrences. Other ways of protecting natural water resources are to enact policies such as the Phase I Environmental Site Assessment (ESA) or its European equivalent Environmental Liability Directive (ELD) (2004/35/EC), which makes property owners liable for contaminations on their properties. The state and local government authorities should be empowered to set up local agencies to enforce the policies of the federal agencies at the grassroots level.

Specifically, there is a need to implement safe abstraction plans with multiple barrier protections practiced globally. Protected areas for pump fields should be defined and isolated from potential contamination sources, as shown in Figure 3. In addition, fixing local water work schemes should be prioritized to guarantee access to safe portable drinking water for the urban poor and the most exposed groups drinking untreated borehole water and sachet water products.

Furthermore, it is imperative for relevant agencies, such as NAFDAC and the Standards Organization of Nigeria (SON), responsible for enforcing the safety of secondary drinking products, to develop sustainable guidelines that ensure regular quality monitoring of the products at both the production and shelf stages. This increases public confidence in these products. Again, the procedure for licensing and approval of secondary drinking water manufacturing should be reviewed, and sentiments removed to ensure that only certified products that meet the recommended MAC values are allowed in the market for people to use. These steps will guarantee better access to potable drinking water, ensure sustainable use of resources, and safeguard public health in the area.

Finally, this study further supports and contributes to the database, which is necessary to provide credible data for advanced modeling approaches at study sites where contamination prevails and helps to remediate or protect the source water in the area.

We appreciate Mary Nthambi for her advice during the questionnaire design and Okechukwu Njoku for logistical support during the field trip in Nigeria. We thank Akuagwu Agbanyim at the Department of Chemistry, Abia State Polytechnic Aba, for granting us access to their laboratory and Christopher Okonkwo for assistance during bacteriological analyses. Finally, we are grateful to the Department of Raw Material and Natural Resource Management and the Graduate Research School at the Brandenburg University of Technology, Cottbus-Senftenberg, for financing the research stay of U.D.I in Nigeria.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.