An efficient low-cost–low-technology whole-household water collection and treatment system Open Access

Human societies inextricably depend on water to efficiently and effectively drive socioeconomic activities for development and wealth creation. Water is considered a human right (UN 2010) and lack of access to safe water adversely affects daily living, gender inequality, health, food security and education (Martínez-Santos 2017). Achieving water sufficiency is the target of many governments of the world, the World Health Organization (WHO) and United Nations (UN). Consequently, laudable global initiatives such as the Millennium Development Goals (MDG), of which target 7c aimed at halving the proportion of the global population without access to safe water, were undertaken to improve water availability (Sambu 2016). Although the goal of MDG 7c was met globally and about 91% of global population have improved water access (Martínez-Santos 2017), 785 million people still lack basic drinking water access and about 2 billion people worldwide use drinking water sources contaminated with faeces (WHO 2019; Wydra et al. 2019). Furthermore, over 829,000 die annually due to waterborne diseases (diarrhea, cholera, hepatitis A, dysentery, typhoid and polio) and poor sanitation (WHO 2019). By implication, access to water alone cannot stop the transmission of waterborne diseases; the water supply must be contaminant-free (safe), reliable, affordable and available when needed to achieve the desired health targets (Martínez-Santos 2017). In acknowledgement, goal 6 of the Sustainable Development Goals (SDG) targets equitable access to safe and affordable drinking water for all by 2030 (Sambu 2016; Thomas et al. 2020). Achievability of this goal is daunting as many cities in developing countries still grapple with the problem of safe water availability.

The problem of safe water shortage is anticipated to worsen in the near future as global water demand is projected to increase by 30%–55% while global renewable water resources will have been reduced by 25% in 2050 (Wydra et al. 2019; Chandran et al. 2021). Unfortunately, cities suffering water shortage contemporaneously exhibit rapid population growth and are more vulnerable to climate change. Africa, especially sub-Saharan Africa, falls within this group and the situation is obfuscated by poor water governance, weak water infrastructure (treatment and reticulation facilities) and policy, dearth of water professionals and technologies, increasing incidence of water pollution and short population doubling time (Martínez-Santos et al. 2020; Niasse & Varis 2020). For example, in 2020, the Nigerian and African populations were estimated at over 206.13 million and 1.34 billion, respectively, and these populations are correspondingly projected to reach 410 million and 2.5 billion (double) in 2050 (Worldometer 2020). Presently, over 19% and 50% of urban and rural dwellers in Nigeria lack access to improved water access (Martínez-Santos 2017). Meeting the safe water demand of future populations in Africa will pose a major challenge to the governments of the region, which are not only overwhelmed by current demands but are also encumbered by several other debilitating socioeconomic problems.

There is therefore need to consider all the viable options for safe, reliable and affordable drinking water supply in order to meet the increasing demand of urban and rural dwellers, and to achieve SDG6. Self-supply is a viable option to access drinking water in many rural and urban areas in Africa (Edokpayi et al. 2018; Silva et al. 2020). Self-supply is the process whereby households or small communities, without access to public water, supply themselves with drinking water. Self-supply is governed by source availability and income (Adelana et al. 2008; Foster et al. 2018) and it is frequently occasioned by rapid expansion of cities without concomitant increase in water facilities. It is estimated that self-supply accounts for over 30% of drinking water supply to urban populations in Africa and South Asia (Silva et al. 2020). Self-supply water is primarily sourced from springs, streams, wells and boreholes (WHO/UNICEF 2017; Lapworth et al. 2020; Thomas et al. 2020; Chandran et al. 2021). Given this significant contribution to water supply, prioritizing self-supply in integrated water management is key to sustainable safe water availability in Africa. However, self-supply could expose consumers to health risks (Edokpayi et al. 2018; Silva et al. 2020), as previous studies have shown that sources are often contaminated with disease-causing pathogens, heavy metals and hardness-causing carbonates (Okogbue & Ukpai 2013; Ngele et al. 2014; Nwonumara et al. 2019; Okogwu et al. 2019; Lapworth et al. 2020). Although self-supply improves access to drinking water, it does not necessarily guarantee access to safe drinking water, resulting in the persistence of the health challenges associated with poor water access.

Consequently, there is need for technologies that can improve the water quality of self-supply water (Martínez-Santos et al. 2020) and such technologies must be capable of effectively eliminating chemical and microbial contaminants in the water. Household water treatment (HWT) is a common practice in areas where pipe-borne water is absent or water supply is of doubtable quality and it can reduce the threat of outbreak of pathogenic waterborne diseases (WHO 2017). Incidentally, most available household water treatment (HWT) technologies focus on point-of-use treatment rather than whole-house water treatment. Such technologies are of limited use as stored water is often recontaminated and some young family members may drink untreated water within the household. Consequently, the need for simple and inexpensive whole-house water treatment technologies capable of providing clean and safe water to the entire household and small communities, daily and throughout the year, is of the essence.

The main aim of this study is to design a simple and affordable water collection and treatment system that effectively removes common water contaminants in self-supply water sourced from borehole and rain in order to improve safe drinking water availability to the entire household. This is exigent, especially in cities like Abakaliki, Nigeria, where the borehole water contains hardness-causing substances, heavy metals and pathogenic microorganisms. Most available point-of-use (POU) water treatment methods such as boiling, filtration and chemical treatment are effective at eliminating only some of the contaminants. In addition, microbial recontaminations occur during storage and some persistent contaminants such as heavy metals remain in the treated water, which could pose serious health risks. Our system is designed to eliminate all contaminants in the water, prevent recontamination and supply safe and affordable water to the entire household throughout the year. It is also our objective to ensure that the technology is affordable to low- and medium-income earners and can be operated by people with little or no formal education.

The study area is Abakaliki, the capital of Ebonyi State, Nigeria. It is located within the southeastern region of Nigeria and has a human population of about 366,400. In this region, the rainy season starts in May and ends in October with average annual rainfall of 1,500 mm (Ngele et al. 2014). Abakaliki is one of the fastest-growing cities in Nigeria with numerous new layouts to accommodate the ever-increasing population. Several water projects by the State government, aimed at improving water supply, fall short of demands and most residents lack access to public water supply. Most households in the new layouts (city extensions) are not connected to the public water supply systems, consequently, self-supply of drinking water from rain and boreholes is very common. In addition, those dwelling in city centres that are connected to the public water supply system receive intermittent supply and still depend on self-supply to remedy water deficit.

Most households of high-income, middle-income and upper low-income earners have existing borehole and/or rainwater collection systems. Regrettably, available information shows that the groundwater in Abakaliki is hard and often contaminated with toxic heavy metals and pathogenic microorganisms (Ngele et al. 2014; Nwonumara et al. 2019; Obasi & Akudinobi 2020). This is attributed to the geology of the area and possible contamination from stormwater running over open defecation areas and seepage from sewage septic tanks. Thus, the water is unsafe for consumption without proper treatment. Unfortunately, most residents consume the water untreated, which could pose public health hazards. Therefore, water treatment technologies that can effectively eliminate the aforementioned contaminants will essentially improve safe water access in the city and improve public health. For the purpose of this study, Amike-Aba, one of the new layouts in Abakaliki, was selected through a random process.

The study was undertaken between November 2019 and October 2020. The treatment system (Figure 1) was designed using materials available in the local market. The plumbing is simple and easily assembled. The treatment system consists of three plastic water tanks (3,000-litre capacity each), rainwater collection funnel and piping, surface pump, two water filters and reverse osmosis unit. During the dry season (November 2019–April 2020), the first tank was filled with groundwater sourced from a borehole, then 8.10 mg/L of alum (KAl(SO₄)₂·12H₂O) was added to the raw water to aid flocculation and thereafter allowed to settle. After four days, 68.21 mg/L of calcium hydroxide (Ca(OH)₂) was added to remove hardness and the water was aerated naturally. After two days, the water was transferred by gravity to the second tank where it was disinfected using 1.875 mg/L sodium hypochlorite (NaOCl) and allowed to stand for two hours before being pumped into the third tank (overhead tank).

The water was then reticulated through gravity to the entire household, passing through an external filter containing a five-micron carbon water filter cartridge, an internal filter (located within the house) containing a 0.5-micron carbon block filter and then a reverse osmosis system. The filter cartridges were replaced as recommended by the manufacturers. Before the installation of new filter cartridges, the supply pipes were flushed with 1.875 mg/L of NaOCl to eliminate possible contaminants. Sludge collected in the first and second tanks was removed at the completion of each treatment cycle to avoid accumulation and re-suspension during the next round of treatment.

During the rainy season (May–October 2020), rainwater was collected from the aluminum roof, filtered into the first tank, and 8.10 mg/L of potassium aluminum sulphate (KAl(SO₄)₂·12H₂O) was added to aid coagulation. After four days, the water was transferred to the second tank, where 1.875 mg/L sodium hypochlorite (NaOCl) was added and allowed to stand for two hours. Thereafter, the water was pumped into the overhead tank and reticulated as described above.

In order to minimize contamination from pipes and collection systems, the borehole was purged for ten minutes before pumping to the first tank while the rainwater was collected two weeks on commencement of the rainy season and after 10–30 minutes (depending on rainfall intensity) during each rainfall.

The efficiency of the treatment system was evaluated by comparing the water quality of the raw with the treated water. To this end, before and after water treatment, duplicate water samples were collected for chemical and microbiological analyses. Raw borehole water was collected from the dispense pipe after ten minutes' purge, while raw rainwater samples were collected directly from the roof after 10–30 minutes of rainfall. Treated water samples were collected from the kitchen tap within the household. In all, 12 duplicate samples each of raw borehole, treated borehole, raw rain and treated rainwater were collected following a stratified randomization pattern that covered the dry (November 2019–April 2020) and rainy (May–October 2020) seasons. Samples for water quality analyses were taken once per cycle of water collection and treatment. Water samples were tested for pH, salinity, conductivity, total dissolved solids, total hardness, chromium (Cr), copper (Cu), lead (Pb), iron (Fe), manganese (Mn), and heterotrophic and coliform bacteria. All analyses were performed in duplicate for each cycle.

The pH, salinity, conductivity and total dissolved solids were tested in situ using Hanna pH (model HI 98108), salinity (model HI 98203), conductivity (model HI 98303) and TDS (model HI 98301) digital meters, respectively. Water samples for total hardness and heavy metal analysis were collected in separate 1 L polyethylene bottles. Total hardness was analyzed by ethylenediaminetetraacetic acid (EDTA) according to the methods of APHA (2012). The samples for heavy metals analyses were preserved with 10 mL analytical grade 1:1 nitric acid:deionized water. The concentration of heavy metals (Cr, Cu, Pb, Fe and Mn) in the water was determined using an atomic absorption spectrometric (AAS) method after digestion as described in Okogwu et al. (2019).

Water samples for microbiological examinations were collected using 250 mL sterile polyethylene sample bottles and stored in a cool box prior to processing in the laboratory. All water samples for microbiological analysis were processed within seven hours of collection. Water samples for heterotrophic plate count (HPC) and total coliform (TC) were analyzed using standard protocols of filtration, incubation and microscopy (APHA 2012). Briefly, 100 mL of the samples for heterotrophic plate and total coliform counts were filtered using a 0.45 μm gridded, 47 mm diameter filter membrane. Since the bacteria density of the water is unknown, to ensure that the number of colonies are within the accepted (20–200 colony forming units (CFU) per membrane) range after incubation (APHA 2012), four different volumes of 25 mL water of each sample were filtered using different membrane filter papers and incubated separately. After incubation, if no filter had bacteria growth within 20–200 CFU, the number of colonies were summed for the four filters and recorded as number per 100 mL. After filtration, the HPC samples were incubated at 28 °C for 5–7 days using R2A agar and TC samples were incubated at 37 °C on m-Endo agar for 24 hours.

Since both coliform and non-coliform bacteria can produce sheen and no sheen, verification of coliforms was done by a lactose fermentation procedure. Five typical and five atypical colonies from a membrane filter culture were transferred to lauryl tryptose broth and incubated at 35±0.5 °C for 48 hrs. Gas formation within 48 hrs verifies the colonies as coliform.

After incubation, the colonies were counted using a low-power (10–15 magnification) binocular wide-field dissecting microscope with cool white fluorescent light source directed to provide optimal viewing of colonies.

Statistical analysis was performed with SPSS version 23, using one-way analysis of variance (ANOVA) to test for significant difference between raw and treated borehole water, and raw and treated rainwater (p<0.05). The efficiency of the treatment system at treating individual variables was calculated as the percentage of the amount of the variable removed after treatment divided by the amount of the variable in the raw water. The amount of variable removed was calculated as the amount of variable in the raw water minus the amount of variable in the treated water. For the heavy metals, we assumed that the amount of metal remaining in the water after treatment was just below the detection limits of the particular metal (i.e. Cr=0.00019, Cu=0.00009, Pb=0.00049, Fe=0.00019 and Mn=0.00009). For pH, percentage reduction was calculated by comparing values in the treated water to 7.0.

The results (Table 1) show that the rainwater was clean and free of microbial contaminants. The rainwater could be consumed untreated without any adverse health effect. Nevertheless, we treated the water knowing that contamination could occur during storage and piping. Our treatment system ensured that contamination during storage and reticulation was prevented, as the reticulated water was contaminant-free. However, the raw groundwater was hard (total hardness = 33.15±23.20 mg/L), alkaline (pH = 8.0±0.01) and contained high amounts of heavy metals, and HPC and TC bacteria as previously reported for Abakaliki (Okogbue & Ukpai 2013; Ngele et al. 2014; Nwonumara et al. 2019). The concentrations of Pb (0.09±0.002) and Cr (0.05±0.002) in the untreated water were above WHO (2017) permissible standards. Daily intake of heavy metals such as chromium (Cr) and lead (Pb) can adversely affect the blood, nervous system, kidney, intelligence quotient of children, immune system, cholesterol metabolism and hormonal balance, and increase the risk of cancer (Jaishankar et al. 2014; Okogwu et al. 2019). Heavy metals can also impair antioxidant activities in living cells, leading to accumulation of reactive oxygen and nitrogen species and consequent oxidative damage (Rehman et al. 2018). Total heterotrophic bacteria units (CFU/mL) and total coliform (MPN/100 mL) of the raw water were 2.7×10³ and 378±21.25, respectively. These exceeded the WHO guideline of zero CFU in drinking water (WHO 2017). Although thermotolerant (faecal) coliform was not studied, a previous study (Ngele et al. 2014) detected Escherichia coli in the borehole water from this area, which together with the high level of heterotrophic and total coliform bacteria observed in this study suggests possible faecal contamination of the raw borehole water. In addition, the presence of coliform bacteria suggests the potential presence of pathogenic bacteria, viruses and protozoa (WHO 2017). The chemical and microbiological water quality render the raw borehole water unsafe for drinking (APHA 2012; WHO 2017; Lapworth et al. 2020). The likely sources of faecal contamination are septic tank sewage disposal systems and stormwater running over open defecation areas, which are common in some parts of the studied area. Further analysis of stormwater in the area could ascertain this postulation.

Exceedance of WHO (2017) water quality criteria for Cr, Pb and TC was observed in 40%, 100% and 100% of the raw borehole water sampled (Figure 2). Consumption of the untreated borehole water could predispose the population to waterborne diseases such as dysentery, diarrhea, typhoid fever and cholera. Occasional outbreaks of these diseases have been reported for the studied area.

After treatment, the pH of the water reduced significantly from 8.0±0.01 to 7.2±0.01, conductivity and total dissolved solids (TDS) reduced significantly by over 90% (p<0.05), all the metals were below detection levels and the microbial contaminants were eliminated from the water. The water quality of the treated water met the WHO (2017) standard for drinking water. Addition of alum (KAl(SO₄)₂·12H₂O) and Ca(OH)₂ improved water clarity and reduced hardness, which also reduced the chlorine demand as widely discussed in the literature (WHO 2017; Moropeng et al. 2018; Rogers et al. 2019). The chlorine dosage used in this study was based on the recommendation of Lantagne (2008) that a 1.875 mg/L dose of NaOCl can effectively eliminate common microbial contaminants in water with turbidity of less than 10 NTU and maintain free chlorine of over 0.2 mg/L after 24 hours.

The treatment system effectively reduced pH (94%–97%), salinity (99%), conductivity (88%–94%), hardness (83%–92%), TDS (91%–96%), heavy metals (99%) and TC (100%) as shown in the box plot (Figure 3). With the exception of conductivity, hardness and TDS, the system effectively improved all water quality parameters, consistently between treatments. Our results showed that a 1.875 mg/L chlorine dose was effective in eliminating microorganisms in the water during storage and reticulation. Transferring the water to the second tank after liming, coagulation and aeration, prior to chlorination, apparently reduced the chlorine demand as most of the non-microbial contaminants were retained as sediments in the first tank. When the quantity of non-microbial chlorine reactive substances (organic and inorganic) in water is high, a large amount of chlorine is required for disinfection. Reduction of chlorine reactive substances reduces chlorine demand and the dosage of chlorine required to effectively disinfect the water (Lantagne 2008; WHO 2017).

The zero heterotrophic plate count and total coliform count observed in the treated borehole and rain water indicate the operational effectiveness of the disinfection process, cleanliness and integrity of the distribution system of our water treatment system as suggested by WHO (2017).

Our water treatment design, which combined coagulation, disinfection and micro- and ultra-filtration, as expected improved water clarity, reduced hardness and heavy metals, and eliminated microorganisms from borehole water. This is consistent with the WHO (2017) position that household water treatment technologies and safe storage can significantly improve water quality and reduce waterborne infectious disease risks. Our design improved water quality by effectively removing the microbial and chemical contaminants found in the raw water. The performance was better or comparable to available POUs such as nanofiltration (Jakubczak et al. 2021), silver-impregnated porous pot filter (Mwabi et al. 2013; Moropeng et al. 2018), chlorination, flocculation, and ceramic and sand filtration (Ngai et al. 2007; Murphy et al. 2010; Omedi & Kipkorir 2010; Mwabi et al. 2013; Arnold et al. 2016; Rogers et al. 2019).

Furthermore, the treatment process completes within six and four days for groundwater and rainwater, respectively. Therefore, meeting the domestic needs of a household of six persons at the WHO recommendation of 50–100 L/capita/day (Thomas et al. 2020) of safe water was readily achieved throughout the year. The annual per capita cost of water treatment (Table 2) using this technology was estimated at N 4,474.44 ($9.32), which compares favourably with the cost of available POU interventions (Ngai et al. 2007; Moropeng et al. 2018; Rogers et al. 2019). Consequently, for a household of six, it will cost N 26,841.60 ($55.92) yearly to treat self-supply water, which is affordable to low- and medium-income earners in the city.

This study strengthens the importance of household water treatment interventions in improving access to clean and safe water.

This simple low-cost water treatment system comprised of liming, coagulation, chlorination, filtration and reverse osmosis effectively removed hardness, microbial and heavy metal contaminants from borehole water. Applying this technology has huge potential of improving safe water availability in Abakaliki and similar cities in developing countries. If incorporated into the integrated water supply policies of government of the region, safe water access by people disconnected from public water supply will improve and there will be significant reduction in waterborne diseases such as diarrhea and cholera. The technology is affordable to low-income earners and can be operated by adults with limited formal education and water treatment skill. The system can be adapted to larger households, different income groups and similar geographical regions.

The authors are grateful to the Department of Applied Biology and Biotechnology Research and Development Centre, Ebonyi State University, Abakaliki, Nigeria, for providing most of the facilities used in this study.

The authors have no conflict of interest.

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