Overview of the low-cost technologies for household water treatment in developing countries

The availability of clean water and sanitation facilities in Sub-Saharan Africa (SSA) has recently improved, leading to a positive change in water governance (Nyika & Dinka 2023). As communities gained better access to clean water and sanitation, they became better equipped to manage their water resources and make decisions about water usage. Unfortunately, indigenous communities were among the hardest hit by the shortage of clean and safe water (Balasooriya et al. 2023). In 2019, only 56% of city-dwellers in SSA countries had access to piped water from water authorities, despite the rapid urbanization and growing population in the area (Armah et al. 2018; Eberhard 2019). Even a slight improvement in safe water access and sanitation facilities had a big difference in reducing the incidence of infectious diseases (Cilliers 2021). In fact, inadequate water, sanitation, and hygiene led to global annual diarrhea deaths of about 58% (Mackinnon et al. 2019).

Africa is rich in water resources available in the ground, such as aquifers, as well as on the surface, such as streams, rivers, springs, and lakes (Mahed 2023). The availability of water sources facilitated various social and economic activities, including household use, irrigation, livestock, and industrial applications. Unfortunately, mostly of social and economic activities contributed to water contamination, which adversely affected water quality. A water contaminant refers to any substance other than water molecules that, when present above a certain threshold, potentially cause harm to humans, animals, or the environment (Sharma & Bhattacharya 2017). Environmental Protection Agency (2023) expressed possible contaminants and infectious diseases, highlighted the importance of protecting water sources and ensured access to clean and safe water for all communities. There are several circumstances in which it may be necessary to treat water at the point-of-use (PoU) or inactivate microbial pathogens, including (i) failure of control measures, including lack of or improper disinfection and unsafe handling and storage; (ii) emergencies and disasters led to inadequate sanitation, hygiene, and protection of water sources (WHO 2015).

Approximately 45.6% of the population in Tanzania lacked access to clean and safe water (Komba et al. 2022). The piped water sources for clean and safe water provision in urban areas were about 60% compared to 28% in rural areas (Musonge et al. 2022). Large parts of urban and rural areas faced acute piped water supply issues due to poor planning, inability to address technical aspects, financial issues, operation, and maintenance (Marobhe 2008). High non-revenue water due to the water losses, high pressure at the nodal junctions, low flow velocity resulting from oversized pipes caused water stagnation, and unreliable water supply services were significant challenges in operations of the water infrastructure of most fast-growing cities in developing countries (Shushu et al. 2021). However, there were initiatives to improve the water supply and reduce the time spent fetching water (Hopewell & Graham 2014).

Various water treatment technologies produced different water quality associated with drawbacks (Kiagho et al. 2016). A slow-sand filter combined with sodium silicate and silver nano-materials purified raw water and applied to only a few indigenous communities in the Northern part of Tanzania (Hilonga 2019). Two non-profit organizations allocated in Morogoro and Arusha region made pot ceramic filters with an average of 99.8% efficiency in removing Escherichia coli and other bacteria with the capacity to produce an average of 50 liters of clean drinking water per day (MSABI 2023; WTW. Wine to Water 2023). Generally, cloth filtration, chlorination–water guards, and solar water disinfection (SODIS) were mainly adopted in developing countries for treating raw water (K'oreje et al. 2020). This paper presents cost-effective water treatment techniques for domestic use in developing countries, with a concentration on cloth filtration, boiling, chlorination, and solar water disinfection (SODIS). It also reviews the treatment effectiveness to eliminate the impurities and associated costs of implementing small-scale water treatment facilities.

Decantation is the process of separating insoluble impurities from raw water by taking advantage of their varying densities, which causes denser contaminants to settle at the bottom of the container (Jorge et al. 2021). The presence of suspended impurities in raw water with a density slightly different or lower than the water density is commonly separated using the flotation technique (Rubio et al. 2007). The injection of air at high pressure into the raw water, forms tiny bubbles, i.e., less than 0.1 mm (Puget et al. 2000). Then, hydrophobic suspended impurities adhere to the bubbles and, moving against the gravitational pull (Kyzas & Matis 2018), rise and accumulate on the surface of the water (Srinivasan & Viraraghavan 2009; Li & Xiao 2023). The flotation technique comprised ejector systems including a pump, heater, mixer, and cooler to generate dissolving air at high pressures in the solid–liquid separation process (Zabel 1984). The application of the flotation technique depended on the quality and nature of effluent particle size down to 10 μm, aerobic sludge, operation flexibility, capital cost, and separation efficiency greater than 90% compared to the sedimentation/decantation technique (Viitasaari et al. 1995).

Filtration is a unit operation that separates suspended impurities in the raw water through a porous medium or membrane (Cheremisinoff 1998). The size of porous media or membrane allows the impurities of the same size to pass and retain larger particle size at a specific time (Ghaedi et al. 2016). A porous media or membrane is a thin interface discrete layer up to the pore size of less than 10⁻⁸ m diameter that moderates the permeation of pressured raw water (Baker 2012). Many of the filters are off-the-shelf market manufactured with four different models: (i) cake filtration involved the hard particulate solids and assumed to settle on the top side of the filter with a constant permeability and pressure drop increased linearly; (ii) blocking filtration involved the constant permeability with the pressure drop increased exponentially; (iii) deep bed or depth filtration involved the retaining suspended contaminants depending on the pore size of the media like any related sand or ceramic filters; and (iv) in cross-flow filtration, the engineered filter media, characterized by precise pore size, is subjected to high-velocity raw water flowing tangentially across it, allowing only a fraction of the liquid to pass through (Abd Rahim & Othman 2019). Examples of cross-flow filtration technologies include microfiltration, ultrafiltration, nanofiltration, and reverse osmosis, as detail described in Ripperger et al. (2000).

Coagulation destabilized the suspended contaminants using coagulants to promote impurities to come together. A coagulant is a chemical product from organic or inorganic materials. A coagulant chemical was added to the raw water to neutralize the negative charges of the non-settled contaminants (Sharma & Ahammed 2023). Flocculation refers to the process in which destabilized particles agglomerate to form larger particles known as flocs. (Ghernaout 2020). Water disinfection means inactivating biological contaminants using physical or chemical disinfectants (Gelete et al. 2020). The physical disinfectants include ultraviolet light (UV), heat, sounds, and other radiations. Chemical disinfectants include chlorination, ozonation, hydrogen peroxide, and metal oxidation processes (Ishaq et al. 2018; Gelete et al. 2020).

The use of a non-woven fabric filter to the conventional-slow-sand filter improved the removal performance of contaminants in the raw water (Mondal et al. 2007). The innovative approach of applying non-toxic polymer coatings to cotton fabric (Kawabata et al. 1992; Zahid et al. 2017), along with the use of engineered fabrics such as Bidim A8 and A10 (Siwila & Brink 2019), and the integration of fabric materials into traditional filters (Siwila 2019), enhanced the adoption of fabric-based materials for cost-effective water treatment in household settings. However, the filter selection depended on the amount of water treated, investment capital, residual discharge, chemical resistance, swelling, heat, pressure, wear, hydraulic and retention rate (Eyvaz et al. 2017).

Boiling small quantities of water into a stove or heater to remove the contaminants has been practiced for many years (Dinkel et al. 2020). The boiling method was the most common means of treating water against alternative household-based filtration methods and disinfection (Clasen et al. 2008). Boiling water effectively neutralized contaminants in the water (WHO 2015); however, this method was not adequately highlighted or consistently implemented within communities. The piped and tap water was safe and potable for drinking whether normal boiled, prolonged boiling, or repeatedly boiled water (Zhai et al. 2020). Boiling water before consumption improved health within communities and reduced the incidence of non-waterborne digestive (Li & Xiao 2023). However, traditional belief that water was typically boiled solely for children, while such boilers acknowledged that boiled water was freed from germs, but not ready to drink (Juran & MacDonald 2014).

The boiling method had the advantage of being widely practiced in households to improve water quality (Zhang 2013). However, it has challenges regarding the cost of energy sources, i.e., wood, charcoal, electricity, or gas (Rosa et al. 2010) or recontamination during storage (Brown & Sobsey 2012), causing accidents to children and burnt houses (Juran & MacDonald 2014). Some pathogens like bacteria, protozoa, and viruses are destroyed at a temperature above 60 °C with a resident time of up to 20 min (Ghaudenson et al. 2021). The boiling process was reported only to remove a small amount of chlorine residual (Bayne et al. 1965). As practiced in boiling or thermal disinfection, pathogens were killed at the temperature ranging from 20 to 90 °C (Espinosa et al. 2020). However, some contaminants including amino acids and nucleotides, are killed at high temperatures above 200 °C (Brock 1985).

Chlorination is the process of adding chlorine to disinfect contaminants in the water. The suspended matter with turbidity below 5 NTU in the water increased the ability of chlorine to react with the pathogens, molds, and algae common in water reservoirs and tanks. Chlorine was applied into the water in several forms as chlorine gas – elemental, sodium hypochlorite solution – bleach, and dry calcium hypochlorite. Chlorine is characterized by versatile and low-cost disinfectant. Chlorination applied to different locations: (i) point-of-delivery – chlorine added into the water truck tank, but care should be taken to avoid corrosion; (ii) in-line chlorination involves continuously discharging chlorine into the water network as distributed to the users; (iii) POU-chlorine was introduced into the clay pot, jerrican, or plastic container, resulting in a chlorine concentration that reached as high as 10 mg/L (Branz et al. 2017). Again, POU treatment is utilized in drilled wells or boreholes (Reed et al. 2013), although the chlorine levels may not remain consistent or diminish quickly (Verkerk & McNicholl 2018).

Chlorine residuals were typically maintained between 0.2 and 0.5 mg/L in commercial water supplies or tap water to ensure the preservation of water quality throughout distribution and storage (WHO World Health Organization). But, it produced challenges of odor and taste concerns for some users (ACC. American Chemistry Coucil 2019). Combining hypochlorous acid and hypochlorite ions made free chlorine (SDWF. Safe Drinking Water Foundation 2023). The interaction of free chlorine with humic and fulvic substances in the water presented an additional issue of forming trihalomethanes (THMs) and other halo-compounds, such as haloacetic acids (HAAs), which are disinfection byproducts (DBPs). However, the best option is to avoid the formation of these compounds, as regular consumption of DBPs can pose health risks to humans (Nair et al. 2023). Following the regulations set by the USA, which limit HAAs to 60 μg/L and THMs to 80 μg/L in tap water, is a good practice to adopt (USEPA US Environmental Protection Agency 2006). As natural organic matter as the major contributor to DBP, other factors like salt composition and concentration increase the formation (Hao et al. 2017). Balancing between the chlorine dosage and reagents helped to minimize the formation of DBPs (Ding et al. 2019) or reduce them to a lower level (Ghernaout 2017).

High formation of DBPs during chlorination requires use of the carbon adsorption treatment plant before water is distributed to the users (Spirenkova et al. 2021). The kinetics formation of the DBPs during chlorination detail described in Cheng, et al. (Cheng et al. 2023). The use of granular activated carbon, quartz and sand treatment (Qiao et al. 2022), advanced oxidation processes (Patton et al. 2022), or ultraviolet/hydrogen peroxide (UV/H₂O₂), and ultraviolet/peroxymonosulfate (UV/PMS) improved the removal of the DBPs in the chlorinated water (Huang et al. 2022). The five commercial sensors such as free chlorine, oxidation-reduction potential, pH, turbidity, and ultraviolet absorbance at 254 nm used to monitor the DBP levels (Reynaert et al. 2023). Again, a lot of literature indicated granular activated carbon was very effective in removing DPB, much more than 25% (Stefán et al. 2019). However, adding TiO₂ and ZnO into the treated water to remove DBPs was possible after exposing to solar radiation (Pérez-Lucas et al. 2022).

Containers or pipe systems with storage were loaded with untreated water and exposed to sunlight to deactivate pathogens. The system of flowing raw water, combined with parabolic concentrated solar power, was engineered to enhance the daily volume of water purified (Meierhofer & Landolt 2009; Preez 2011). Positioning the bottles on a black surface (Haider 2017) and corrugated metal sheets (Karim et al. 2021) created a temperature gradient that boosts the efficiency of pathogen inactivation.

The raw water with a high oxygen level increased the chance of microorganisms being inactivated with solar radiation. The bottles were filled with raw water for about three-quarters, shook about 20 seconds for the aeration process, and closed the bottle with the lid before being exposed to solar radiation (Meierhofer & Wegelin 2002). Robust and inexpensive indicators such as photodegradable dye-based, polyoxometalate, and semiconductor photocatalysis were added into the raw water and indicated a significant color change when exposed to solar energy of 389 kJm⁻² (Lawrie et al. 2015); equivalent to the energy required to inactivate the pathogens (Martínez-García et al. 2023) and fungi (Farhadi et al. 2022). The indicators show that the raw water is ready for drinking. The use of nanotechnology in the SODIS accelerated the elimination of microorganisms. The performance of SODIS was improved using the photocatalyst of TiO₂, silver, copper (Nalwanga et al. 2014), and natural clay (Verma & Prasad 2013).

This paper highlights the importance of low-cost household water treatment techniques for developing countries, including cloth filter, boiling, chlorination and solar water disinfection. Low-cost technologies inactivated the microorganisms and related contaminants with simplicity to fit the individual community. This review emphasized the potential of proper choice of cloth materials would improve the initial step of treating high turbidity water using preferable woven fabric with the interlacing pattern. The use of boiling techniques faced the challenges of unclean burning fuels, recontamination and burning of property. The application of chlorination faced the challenges of improper dosage of chlorine with minimum residual level and DBPs at the point-of-use. The use of solar water disinfection faced the challenges of water depth corresponding to the level of turbidity, residence time to expose the bottle on the sunlight, improper water bottle materials, additive costs and detection limits for inactivation of microbials.

The Benjamin W. Mkapa Fund supported this work through the University of Dodoma under the junior research grant category.

Authors originated and conceptualized the idea, O.J.M. designed the research and drafted the paper outline, A.L. and N.S. contributed equally to research design and manuscript compilation.

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

The authors declare there is no conflict.