Commercial reverse osmosis point-of-use systems in Egypt failed to purify tap water

Access to clean water is crucial for human health and societal well-being. Historical methods of water purification, documented in ancient Sanskrit and Egyptian texts, include boiling, solar heating, and sand filtration (Blake 1956). Water is vital for sustaining life, supporting agriculture, fueling industrial processes, and facilitating daily domestic tasks. Despite the availability of clean, potable water in developed areas, more than 30% of people in less-developed regions lack access to this crucial resource (Pooi & Ng 2018). Thus, achieving universal access to reliable and safe water supplies remains a fundamental goal for enhancing global health and well-being (Yaghoubi et al. 2020).

With rising concerns about polluted drinking water sources and growing consumer awareness, the urgent necessity for communities to secure and produce safe water has intensified. The PoUs primarily include activated carbon filters, membrane filters, and UV disinfection systems. This multi-barrier approach effectively addresses a broad range of contaminants that no single system can entirely mitigate (Sobsey et al. 2008; Panagopoulos & Giannika 2022a; Panagopoulos 2023). In recent years, PoUs, also known as household water treatment devices, have gained immense popularity (Yaghoubi et al. 2020). These devices are designed for the treatment of a restricted volume of contaminated water, primarily for drinking and cooking purposes. Their cost-effectiveness and capacity to meet the needs of small groups make them apt for short-term responses (Labhasetwar & Yadav 2023). The rising demand for such devices is evident, especially in regions like the Far East, Middle East, and other developing nations (Sobsey et al. 2008; Chen et al. 2020), with the global PoU device market expected to reach 34.1 billion US dollars by 2025 (Chen et al. 2021).

The PoU water treatment sector features a diverse range of systems, each characterized by its cost, materials, complexity, and effectiveness (Clasen et al. 2007). Among these, a prominently adopted PoU technology utilizes reverse osmosis (RO). This method involves a semi-permeable membrane designed to extensively filter out a broad spectrum of impurities from water. The literature recognizes RO's capability to produce high-quality water, albeit with certain limitations (Kajitvichyanukul et al. 2011; Wu et al. 2021). Numerous studies have underscored the efficiency of RO PoU systems in eliminating various contaminants, including pathogens, heavy metals, salts, and specific organic compounds (Fox 1989; Nghiem & Schäfer 2004; Liu et al. 2019; Wu et al. 2021). In addition, RO filters can effectively remove fluoride, which is challenging for many other types of filters (Nghiem & Schäfer 2004). However, these benefits come with challenges, such as high operational costs, water wastage, environmental concerns, and the removal of essential minerals (Chen et al. 2021; Wu et al. 2021).

The operation and maintenance of RO filters incur substantial costs, primarily due to the significant energy requirements for water pressurization and the necessity for periodic membrane replacement (Wu et al. 2021). Nevertheless, PoU devices are effective in filtering out dissolved solids and microbes (Peter-Varbanets et al. 2009; Fahiminia et al. 2014). Some studies highlight potential health risks associated with the RO system's demineralization of water (Kozisek 2020; Labhasetwar & Yadav 2023). Additionally, a drawback of PoU RO filters is their inefficiency, with 40–60% of processed water being wasted. This rejected water, high in total dissolved solids (TDS) and pollutants, poses a threat to sewer systems, treatment plants, and the environment, especially in water-scarce regions (Melián-Martel et al. 2013). The discharge of brine with elevated TDS levels into ecosystems necessitates urgent solutions due to its potential negative impact on aquatic life (Panagopoulos 2022). A promising approach is the extraction of valuable ions such as Na⁺, Cl⁻, Mg²⁺, and Ca²⁺ from the brine, turning waste into useful materials and reducing the environmental footprint of desalination (Panagopoulos & Haralambous 2020; Panagopoulos & Giannika 2022b). Additionally, the disposal of spent plastic filters from RO systems exacerbates their environmental impact (Frank et al. 2019; Sola et al. 2020). Therefore, developing recycling and reuse strategies is crucial (Labhasetwar & Yadav 2023).

PoU devices, if not maintained appropriately, can degrade tap water quality by acting as reservoirs for contaminants that foster microbial growth and biofilm formation. Disturbances in the plumbing system can release these contaminants into the tap water, posing health risks (Nriagu et al. 2018). Most RO units require a drainage system to discard impurities. The primary filtration component, RO membranes, is prone to damage and rupture. Factors like hot water exposure and chlorine can damage or reduce the lifespan of these membranes, while a ruptured membrane might inadvertently allow bacterial contamination. Identifying a compromised membrane can be challenging, necessitating electronic monitoring for optimal functionality. Ensuring the consistent performance of RO systems demands regular monitoring and maintenance, often requiring specialized technicians (Wu et al. 2021).

Research on the water quality produced PoU systems has been limited, with studies primarily conducted outside of Egypt (Chaidez & Gerba 2004; Fahiminia et al. 2014; Chen et al. 2021; Wu et al. 2021). This gap in the literature is notable given the significant variations in water quality observed across different countries. Existing research has focused on evaluating PoUs with respect to physicochemical parameters and heavy metals (Elfil et al. 2007; Fahiminia et al. 2014), specific ions such as fluorides (F⁻) and nitrate (Badeenezhad et al. 2019), or through microbiological analyses (Chaidez & Gerba 2004). Our study extends this body of work by assessing PoUs from a comprehensive perspective that includes physicochemical, bacteriological, and protozoological evaluations, areas previously unexplored in the context of Egypt. Particularly in the Menoufia governorate (Egypt), where more than 1% of urban and 15% of rural residents lack access to clean water (El Bahnasy et al. 2014). Various challenges, including groundwater contamination from sewer systems, ageing water networks, high concentration of iron and manganese, inadequate chlorine treatment and occasionally, a lack of sufficient pressure in the drinking water network, contribute to this problem (El Bahnasy et al. 2014). Consequently, many residents resort to alternative water sources like PoUs, bottled water, or non-governmental water purification stations (El Bahnasy et al. 2014). Despite the widespread adoption of point-of-use (PoU) systems in this region, their effectiveness, and the quality of the water they produce have not been extensively studied. Addressing this gap, our study aims to conduct a thorough evaluation of 10 PoUs, assessing the water quality at both inlets and outlets through physicochemical, bacteriological, and protozoological parameters. This evaluation aims to confirm the effectiveness of PoU systems in reducing public health risks associated with potential contaminated water sources.

The sampling plan targeted 10 RO PoU brands dominant in the Egyptian market (Menoufia province, Egypt), chosen for their representation of systems commonly utilized in the region. Each PoU was anonymized and labeled from 1 to 10 to ensure impartiality and objectivity. In total, 80 water samples were collected from the 10 commercially RO PoUs (referred to as PoU1-1–PoU-10) from different households at both the inlet point (i.e., 40 tap water samples) and post-filtration point (i.e., 40 filtered water samples). The sampling involved four sampling events over 4 months for each PoU (i.e., inlet and outlet).

The methodology implemented in this study adheres to the guidelines established in the APHA's Standard Methods for the Examination of Water and Wastewater (APHA 2017). This involves the laboratory analysis of chemical, physical, and biological properties of water samples collected from both inlet and post-filtration points. Prior to sample collection, tap outlets were sanitized using a flame torch. For the analysis of physical and chemical properties, water samples were collected in 1-L polyethylene containers from both the inlet and post-filtration points. For bacterial analysis, samples were collected in 500 mL glass bottles, which were thoroughly washed with distilled water and sterilized in an autoclave. These bottles were also pre-treated with sodium thiosulfate to neutralize any residual chlorine. The volume of water samples for protozoa analysis was 1 L from each point. To ensure the integrity of the samples, they were transported to the laboratory in an ice box, maintaining a temperature that preserves their physical, chemical, and biological characteristics until analysis.

Physicochemical analyses were performed for 80 water samples (40 tap water samples and 40 filtered water samples) according to the Standard Method for the Examination of Water and Wastewater (APHA 2017). The temperature was measured in situ with a digital thermometer and pH with Bench Top pH/Ion Meter (Model No. 3510, Jenway Instruments, UK). Residual chlorine (free Cl₂) was measured in situ with a digital colorimeter using diethyl p-phenylenediamine (DPT) tablet. Electric conductivity (EC) and TDS were measured using a Bench Electrical Conductivity Meter (Model No. 4510, Jen Way Instruments, UK). Total hardness and Ca were measured by titration with 0.01 N EDTA. Mg was calculated by the difference between total hardness and calcium hardness. Bicarbonate ion (⁠⁠) was measured by titration with H₂SO₄. Nitrate (NO₃), nitrate nitrogen (NO₃-N), ammonia (NH₃), ammonia nitrogen (NH₃-N), and phosphorus (P) were measured using test kits with a NANOCOLOR Macherey-Nagel Photometer (Model No.500D, Germany) according to the manufacturer's protocols. Sulfate (SO₄) was measured by using assay colorimetric kits (Spectrophotometer Hach, DR5000, Germany) according to the manufactures' protocols. Chloride Cl⁻ was measured by titration with AgNO₃. Iron (Fe) and manganese (Mn) were determined using a specific photometer (Avanta E, Model GBC.Avanta, UK) according to the methods manual No. 01-0202-00.

Total coliform (TC), fecal coliform (FC), and Escherichia coli (E. coli) were determined using the membrane filtration method (APHA 2017) using 0.45 mm pore size filters (Gelman Science Laboratories, Ann Arbor, MI, USA). 100 mL samples were collected separately for enumerating total coliforms and an additional 100 mL for fecal coliforms. Membranes were placed onto m-Endo at 37 °C and m-Fc agar at 44.5 °C for 24 h, respectively. The results were expressed in terms of colony forming units (CFU) per 100 mL. E. coli produces yellow or yellow-brown colonies on a filter pad saturated with urea substrate broth after primary culturing on M-TEC medium.

For free-living amoebae (FLA), the water samples were concentrated using nitrocellulose membrane (0.45 μm pore size and 47 mm diameter), cultivated on non-nutrient seeded with heat-killed E. coli, and incubated at 30 °C (HPA 2014). The DNAs were extracted from the morphologically positive samples for FLA using the DNeasy PowerLyzer PowerSoil Kit (QIAGEN, USA) according to the manufacturer's instructions (Gad et al. 2023). The extracted DNAs were subjected to PCR analysis using generic primers (JDP1 and JDP2) (Schroeder et al. 2001) and (Nae-F and Nae-R) (Taravaud et al. 2018) for identification of Acanthamoeba species and Naegleria species, respectively (Table 1). Vermamoeba Vermiformis was identified using HART-F and HART-R (Kuiper et al. 2006). Each PCR reaction was carried out in a final volume of 25 μL, comprising 12.5 μL of master mix (Promega, USA), 3 μL of template DNA, 1 μL each of forward and reverse primers, and the volume was completed to 25 μL using RNase-free water. The amplification program included an initial denaturation at 95 °C for 5 min, followed by 35 cycles; each consisted of denaturation at 94 °C for 30 s, annealing at 55 °C for 40 s and extension at 72 °C for 40 s. The program included a final extension step at 72 °C for 10 min to generate amplification (Schroeder et al. 2001; Marouf et al. 2021). The PCR products were subjected to purification using a GeneJET PCR Purification Kit (Thermo Scientific, USA) according to the manufacturer's instructions. The purified DNAs served as templates for DNA sequencing using the ABI PRISM^® automated DNA Sequencer to identify different FLA strains. Nucleotide sequences were analyzed using the BLAST analysis tools (http://www.ncbi.nlm.gov/BLAST). Gene sequences were prepared using the Bio-Edit program and aligned using Clustal Omega implemented in the EMBL-EBI website (https://www.ebi.ac.uk/Tools/msa/clustalo/), and a phylogenetic tree is created using the neighbor-joining algorithm. Phylogenetic tree was visualized using the Interactive Tree Of Life (iTOL) (https://itol.embl.de/tree/).

The Kaiser–Meyer–Olkin (KMO) and Bartlett's sphericity tests (eigenvalues >1, and absolute r > 0.8 as a criterion) were performed to extract the main components explaining the variance of the environmental variables from the principal component analysis (PCA). The PCA was used to characterize the main environmental parameters in various environments (i.e., tap water and filtered water). Permutational multivariate analysis of variance (PERMANOVA) and analysis of similarity (ANOSIM) assessed significant differences in physicochemical parameters between tap and filtered water samples. PERMANOVA is a robust, non-parametric method that evaluates variance within a dataset to discern if categorical groupings, such as tap versus filtered water, have a statistically significant impact on the observed outcomes. In parallel, ANOSIM operates as a complementary non-parametric technique, which systematically tests the extent of dissimilarities across distinct groups (i.e., tap water and filtered water) to ascertain the presence of significant variations between them. The impact of each PoU on specific parameters was evaluated using the Wilcoxon statistical test. This non-parametric method is used to compare two paired groups, in this scenario, to understand how each PoU impacts the water quality parameters in the filtered water compared to the original state in tap water. The statistical analyses and visualization were performed using PRIMER v.7.0.21 (Quest Research Limited, Auckland, New Zealand) and R v4.1.0 (https://www.r-project.org/).

The global uptrend in the adoption of PoUs is driven by multiple factors, including a growing concern over declining water quality amidst an era of deteriorating infrastructure. The escalating risk of contamination, amplified by burgeoning industrial and urban activities, alongside an increased awareness of waterborne diseases, further fuels the demand for PoUs (Wu et al. 2021). Despite their potential for water treatment, a significant concern arises from the lack of stringent testing and certification for these devices. This deficiency leads to the inadvertent purchase by well-intentioned consumers of PoUs that may not perform as claimed by manufacturers. The prevailing lack of consumer awareness regarding the specificity of different filter technologies for various contaminants further compounds this issue (Hodgkinson 2017). Our study revealed that many PoUs effectively eliminated undesirable elements, such as Fe and Mn, from tap water. Yet, crucial minerals like Mg and Ca were also notably diminished in the filtered water of most PoUs assessed. Additionally, there was a marked decrease in TDS and EC. These observations echo those of a previous study (Badeenezhad et al. 2019). A safety consideration is that water treated with RO, being devoid of minerals, poses potential health risks and it has a corrosive effect on metal piping, and as such cannot be pumped through galvanized or copper pipes (McFeters 2013).

RO stands as a favored water treatment method wherein a pressure differential across a semi-permeable membrane effectively separates dissolved solids from the water supply. This membrane permits the passage of water while obstructing dissolved ions, molecules, and larger particles. The exerted differential pressure propels the water through the membrane, retaining the dissolved contaminants and thereby enhancing the water's quality. Beyond this, the membrane potentially acts as a defensive barrier against numerous microorganisms. Despite these benefits, the efficacy of the RO system hinges on the membrane's integrity. A compromise in this barrier, due to water pressure fluctuations or microbial degradation, could markedly diminish the treatment's effectiveness, rendering the water unprotected against contaminants and microorganisms (McFeters 2013).

This study underscores the elevated concentrations of bacterial indicators in filtered water from several PoUs, compared to tap water. Filter membranes and nearby internal faucet surfaces may unintentionally become grounds for both pathogenic and non-pathogenic microorganisms' growth (Synder et al. 1995; Eichler et al. 2006; Payment et al. 2010). A scant number of trapped microbial colonies within PoU devices can swiftly evolve into biofilms, producing extracellular polymeric substances even in nutrient-deficient environments (Yang et al. 2013). These biofilms, especially harboring pathogens, hold significant public health consequences (Bressler et al. 2009; Feazel et al. 2009). Nriagu et al. (2018) also discovered a diverse bacterial community in the filtered water and inside the PoU unit, comprising species affiliated to Proteobacteria and Firmicutes, with the specific presence of Actinobacteria in filtered water. In the absence of diligent maintenance and timely replacement, PoUs can inadvertently morph into microorganism hotbeds (Massieux et al. 2004). Our study findings indicate a lack of awareness among users regarding the maintenance and operational principles of these systems. Specifically, users generally did not have accurate information about the treatment process, nor did they follow the recommended schedule for cleaning and replacing filters and membranes. Regular washing and cleaning of the treated water reservoir, crucial for preventing biofilm formation and bacterial regrowth, were also not commonly practiced. This lack of proper maintenance could indeed contribute to increased bacterial load. Corroborating our observations, past research shows lower Aeromonas hydrophila, acid-fast organisms, HPC bacteria, Pseudomonas aeruginosa, and coliform levels in tap water without PoU devices compared to treated water (Chaidez & Gerba 2004). This decline in bacterial quality in PoU permeate accentuates the necessity for additional post-treatment stages, such as UV irradiation. While PoUs utilizing a carbon filter, akin to our study, prove effective in removing numerous contaminants, including organic and particulate substances, their efficacy may be ephemeral. After passing through an activated carbon filter in PoU devices, water is expected to show a one to two-log increase in bacterial densities (Taylor et al. 1979). This observation is bolstered by Wallis et al. who reported a spike in bacterial levels within such devices after a short non-use period (Wallis et al. 1974). Consequently, timely filter replacement, determined by the filter's service life and volume of processed water, is imperative.

The diminished levels of certain parameters by RO PoU devices in drinking water can be advantageous, yet the removal of crucial elements such as residual-free chlorine is concerning as it can lead to biofilm development. In this research, all tested PoU devices produced water with residual-free chlorine levels below the standards set by both WHO and Egypt. Such a deficit is critical as it undermines the water's defense against potential secondary contamination and biofilm growth. The reduction in residual chlorine within water distribution system and storage tanks is known to stimulate the resurgence of microorganisms (Liu et al. 2010). This study's survey highlighted a prevalent inability among users to change the filters of PoU devices timely, causing excessive filter usage and fostering bacterial buildup within the devices. This situation augments microbial pollution in the treated water, heightening health risks to consumers (Badeenezhad et al. 2019). Despite the robust filtration capability of RO membranes, a fraction of bacteria might still permeate through minuscule flaws or evade the membrane altogether through tiny seal leaks. A multitude of bacteria can be present in drinking water. While many pose no direct threat, numerous opportunistic pathogens could present health risks (Rusin et al. 1997). Their proliferation within distribution systems or household taps is influenced by various factors including disinfectant levels, season, and the load of organic matter (So et al. 2017; Nescerecka et al. 2018).

The investigation into the microbial quality of water generated by Point-of-Use (PoU) devices uncovers significant concerns surrounding public health and safety. This research reveals, for the first time, the presence of potential pathogens, including Vermamoeba vermiformis and specific Acanthamoeba genotypes (T4, T3), in the filtered water of PoUs, marking a notable discovery in the field. Our study acknowledges that the absence of Naegleria fowleri does not necessarily indicate its actual absence, but rather reflects the limitations of our incubation temperature for its growth. Moreover, the presence of N. clarki in our samples does not necessarily indicate a health concern or suggest an environment conducive to N. fowleri growth. FLA, primarily found in diverse environments like water, soil, and air, emerges as an unforeseen contaminant in drinking water systems, contributing to the formation of resilient biofilms. This development raises alarms as these biofilms, robust and resistant to chlorine, become breeding grounds for bacteria that are notoriously difficult to eliminate (De Beer et al. 1994; Matz & Kjelleberg 2005; Yli-Pirilä 2009; Thomas & Ashbolt 2011; Goudot et al. 2012; McFeters 2013; Malaka 2014; Atanasova 2018). The result is an elevated health risk, underscored by the FLA's known pathogenicity, leading to serious diseases such as encephalitis and keratitis (Trabelsi et al. 2012; Król-Turmińska & Olender 2017). Furthermore, their role as reservoirs for amoeba-resisting bacteria (ARB) exacerbates the potential for harm, particularly in vulnerable environments like hospitals and water treatment plants. For consumers seeking to ensure water safety and quality, the selection of PoU systems must be meticulous (Greub & Raoult 2004; Loret & Greub 2010; Cateau et al. 2014). Opting for systems equipped with features such as automatic flushing, pre-filters for suspended particle removal, built-in disinfection mechanisms, and automatic shut-off is paramount. Such comprehensive features not only enhance the water's safety profile but also actively contribute to the overarching goal of safeguarding public health from unseen microbial threats.

The efficacy of PoUs in water purification presents a multifaceted picture. Through PCA and support by robust statistical tests (PERMANOVA, R² = 0.58, p < 0.001; ANOSIM, R = 0.476, p < 0.001), our research demonstrates marked improvements in water quality, particularly in the significant alteration of the water's chemical composition. Notably, we observed a reduction in TDS from an average of 210 mg/L in tap water to 21 mg/L in filtered water for specific PoU systems, illustrating their profound impact. Despite their competence in eliminating undesired elements such as Fe and Mn, these systems inadvertently reduce crucial minerals like Mg and Ca, leading to a potential mineral imbalance in the filtered water. Moreover, an alarming presence of bacterial indicators, notably coliforms, and the unexpected detection of potential pathogens like Vermamoeba vermiformis and Acanthamoeba genotypes (T4, T3) in the PoUs' treated water demand immediate attention. All tested PoUs failed to meet the Egyptian standards for drinking water (458/2007) from a microbiological perspective. The observed decline in the quality of filtered water could potentially be ascribed to microbial regrowth within the filter tanks. This issue is likely exacerbated by the prolonged utilization of PoU systems, compounded by a lack of consistent maintenance and adherence to the manufacturer's guidelines for filter replacement. Additionally, the unregulated quality of commercially available PoU filters may also contribute to this deterioration. Despite these challenges, our study does not advocate for the discontinuation of PoUs. Instead, it emphasizes the urgent need for informed utilization, underpinned by rigorous, continuous assessments, adherence to regular maintenance schedules, and significant design enhancements focused on maintaining mineral balance and improving microbial filtration efficacy. Further research on the long-term health implications of these filtration systems is essential.

This paper is based upon work supported by the Science, Technology and Innovation Funding Authority (STDF), Egypt, Grant number 44201. Dr Anyi Hu is supported by the National Key R&D Program of China (2022YFE0120300).

M.G. rendered support in methodology, formal analysis, data curation, visualization, writing the original draft, resources, funding acquisition, and writing the review and editing it. M.A.F. rendered support in investigation, methodology, writing the review and editing it. A.A. rendered support in conceptualization, investigation, and methodology. A.H. rendered support in conceptualization, validation, writing the review and editing it. N.N. rendered support in investigation, methodology, resources, writing the review and editing it.

The cooperation with Dr Anyi Hu is under an agreement between the National Research Centre (Egypt) and the Institute of Urban Environment, Chinese Academy of Sciences (China).

All relevant data are included in the paper.

The authors declare no conflict of interest.