Mohammad Alotaibi
Hanan Al-Khalaifah- Environment and Life Sciences Research Center, Kuwait Institute for Scientific Research, Safat, Kuwait
Solar water disinfection (SODIS) is an emerging, sustainable method for improving water quality in regions facing limited access to safe drinking water, including the Middle East and North Africa (MENA). SODIS has been applied to a wide range of microorganisms, which show varying levels of sensitivity to the treatment. Dormant forms, such as spores and cysts, are typically more resistant to inactivation, while bacteria are, in general, more susceptible and can be inactivated within 1 h, depending on solar irradiance intensity. The higher the solar radiation, the faster the inactivation process. Virus inactivation by SODIS follows a pattern similar to that of bacteria, although MS2 bacteriophage is more resistant than both bacteria and other viruses. While some microorganisms require extended exposure times (up to 6 h), certain additives or methods can significantly reduce the time needed for effective disinfection. For example, hydrogen peroxide (H2O2), which forms via reactive oxygen pathways, acts as an oxidative agent, damaging DNA and contributing to the inactivation process. Singlet oxygen (1O2), a key reactive species, is responsible for oxidizing proteins and breaking down DNA and RNA strands, leading to microbial cell death. Overall, SODIS is an effective, low-cost, and simple method for pathogen inactivation, requiring minimal skills and equipment, making it particularly useful in disaster-stricken areas such as those affected by earthquakes or other natural disasters. Its accessibility and effectiveness make it particularly valuable in disaster-stricken areas and resource-limited settings, providing a practical strategy for reducing waterborne disease risks in the MENA region.
1 Introduction
It has been reported that over 4.4 billion people, more than half of the global population, still lack access to safely managed drinking water services, with many relying on unimproved or contaminated sources (UNICEF, 2025; GreenMatch, 2025). Approximately 440,000 children under five die each year from diarrheal diseases due to unsafe drinking water, sanitation, and hygiene (UNICEF, 2024). Various pathogenic viruses, such as poliovirus, can survive and remain infective in drinking water for approximately 7–21 days, with many studies citing around 11 days under typical environmental conditions [Gundy et al., 2009; World Health Organization (WHO), 2024a]. Only about 1.2% of freshwater on Earth is readily available for human use, as the vast majority is locked in glaciers, ice caps, or deep underground aquifers (United States Geological Survey, 2023). It was reported that 26% of the world's population does not have water sterilization facilities.
Most deaths from waterborne disease occur in developing countries, where limited access to clean water, lack of sanitation facilities, and poor hygiene leads to the deaths of approximately 1 million people each year [World Health Organization (WHO), 2022; UNICEF, 2023]. The Middle East and North Africa (MENA) region is one of the most water-scarce areas in the world, with over 80% of the population living in regions facing significant water stress (Conroy et al., 2001; Bonetti et al., 2022). Rapid population growth, urbanization, and climate change have exacerbated water scarcity in the MENA region, compounded by its arid climate, limited freshwater, and groundwater over-extraction, which severely affect rural and marginalized communities (World Bank, 2023; Carnegie Endowment for International Peace, 2024; Daily News Egypt, 2023).
Due to water scarcity, waterborne diseases are of significant concern, as untreated water is often the only available resource for many families. Pathogens such as Escherichia coli, Salmonella, and rotaviruses can spread through contaminated water, posing serious risks to human health. Unsafe water, lack of sanitation, and poor hygiene are responsible for thousands of preventable deaths in the region, particularly among children [World Health Organization (WHO), 2023]. Many rural areas continue to lack access to the infrastructure and financial resources needed for advanced water treatment technologies. Although methods such as boiling remain effective, they require significant time and fuel, placing additional burdens on households already facing energy and resource scarcity (UNICEF, 2023). Therefore, there is a critical need for low-cost, effective water treatment solutions that can be implemented in resource-limited settings to reduce the burden of waterborne disease. In addition, having access to technology that ensures water safety and helps limit the spread of pathogens in the event of environmental catastrophes like earthquakes would be extremely beneficial. Solar water disinfection (SODIS) has demonstrated a positive impact against the waterborne zoonotic parasite Cryptosporidium, which poses a significant health risk due to its ability to infect both humans and animals, making it a major public health concern (Lau et al., 2005; McGuigan et al., 2012; Fayer, 2004). However, the high resistance and infectivity of Cryptosporidium oocysts highlight the importance of proper SODIS implementation, as inadequate solar exposure, high turbidity, or inappropriate treatment conditions may lead to incomplete inactivation and potential residual health risks. Therefore, careful control of operational parameters and adherence to recommended safety guidelines are essential to ensure effective pathogen removal and to safeguard public health.
The SODIS method involves filling transparent polyethylene terephthalate (PET) bottles with microbiologically contaminated water and exposing them to direct sunlight for at least 6 h. The effectiveness of SODIS relies on the synergistic effects of solar ultraviolet-A (UV-A) radiation (320–400 nm), dissolved oxygen, and thermal heating. UV-A radiation penetrates the water, inducing direct damage to the nucleic acids of pathogens and triggering the generation of reactive oxygen species (ROS), such as superoxide (), hydrogen peroxide (H2O2), hydroxyl radicals (•OH), and singlet oxygen (1O2). These ROS inflict oxidative stress on microbial cells, damaging DNA, proteins, and lipids, thereby preventing replication and survival (Sichel et al., 2009; Baier et al., 2006; Davies, 2003; Triantaphylidès et al., 2008). Thermal heating further enhances the disinfection process by raising the water temperature, which accelerates microbial inactivation. The presence of oxygen significantly contributes to these effects, as it the essence in ROS formation under UV exposure. Through this combined mechanism, SODIS has demonstrated high efficiency against a wide spectrum of pathogens, including bacteria (Escherichia coli, Vibrio cholerae), viruses (e.g., rotaviruses), and protozoa (Giardia lamblia, Cryptosporidium parvum; McGuigan et al., 2012; Triantaphylidès et al., 2008). Studies indicate that a minimum solar irradiance of approximately 500 W/m2, or a cumulative UV dose of ~2,000 kJ/m2, is generally required to achieve effective pathogen inactivation within 6–8 h under natural sunlight (Heaselgrave and Kilvington, 2012; Sichel et al., 2007). The SODIS method is most effective for water with turbidity levels below 30 NTU (Dawney and Pearce, 2012), as higher turbidity significantly reduces UV penetration and shields pathogens from inactivation. Pre-treatment, such as sedimentation or filtration, may be necessary for highly turbid water to ensure sufficient disinfection. Therefore, careful control of operational parameters and adherence to recommended safety guidelines are essential to ensure effective pathogen removal and to safeguard public health.
SODIS has been endorsed as a safe and appropriate technology for treating drinking water at the household level in low-resource settings [World Health Organization (WHO), 2011; Luwe et al., 2025]. One of the key advantages of SODIS is its scalability and adaptability to different environmental and social conditions. It can be used in both rural and urban settings, and its simplicity makes it accessible to individuals with minimal technical knowledge or resources. The MENA region presents a unique opportunity for the widespread adoption of SODIS, given its abundant solar resources and the pressing need for cost-effective water treatment solutions. Many countries in MENA receive high levels of solar irradiance throughout the year, making solar energy a highly viable option for water disinfection. Rural areas, in particular, stand to benefit from SODIS, as they often lack access to centralized water treatment facilities and rely on untreated water sources, such as rivers, lakes, and wells. Furthermore, the economic feasibility of SODIS aligns with the needs of communities facing financial constraints. In comparison to other water treatment technologies, SODIS requires minimal investment and operational costs (estimated by $0.63 per person per year), making it an attractive solution for regions where financial resources are limited (García-Gil et al., 2021). Its environmental sustainability, coupled with its effectiveness in reducing pathogens, makes SODIS a key candidate for improving water safety in MENA. However, there are challenges to its widespread adoption in the region. Factors such as water turbidity, cultural acceptance, and seasonal variations in sunlight availability can impact the effectiveness of SODIS and its implementation (Dawney and Pearce, 2012). Therefore, addressing these challenges through education, research, and policy support is critical to ensure the successful adoption and scaling of SODIS in MENA.
Despite the well-documented success of SODIS in various regions of the world, there remains a significant gap in the research and application of SODIS in the MENA region. Current literature lacks a detailed examination of how SODIS can be integrated into existing water management strategies, particularly in rural areas where access to centralized water treatment facilities is limited. Additionally, there is a shortage of research on public perception and cultural barriers to the widespread adoption of SODIS in this region, an area critical for the successful implementation of any water treatment solution. Given the unique environmental, social, and economic conditions of MENA, there is a timely need for a comprehensive review that specifically addresses SODIS potential, scalability, and long-term sustainability in the region. Therefore, the present review aims to explore the mechanism of SODIS, its potential application in the MENA region, its advantages and limitations, and its potential as a scalable solution for water treatment. Through a comprehensive analysis of existing research and case studies, this review aims to provide a detailed understanding of how SODIS can contribute to solving the water challenges in MENA, offering a pathway toward sustainable and affordable water safety.
2 Mechanism of SODIS
Although many studies were performed on inactivation of microbial pathogens using SODIS, one of the first studies of SODIS was carried out by Acra et al. (1980). The authors contaminated an oral rehydration solution (chlorine free) with fresh sewage. The solution was divided into three sterile polyethylene bags, each containing one liter of oral rehydration solution. The first bag was subjected to sunlight, the second was kept in a room under artificial light, and the third was kept in the dark. The starting coliform number was 165 CFU/ml. Under direct sunlight, the coliform number started to reduce after the first 30 min and all bacteria were completely inactivated after 2 h. In the room with artificial light and in the dark the number of coliforms decreased by 80%, indicating the efficacy of SODIS. No re-growth of the bacteria was seen later in the sample that was under direct sunlight, suggesting that long-term storage of the solution would be possible (Acra et al., 1980). The mechanism of action of SODIS is primarily based on the combined effects of solar UV radiation and heat (Figure 1). UV radiation, especially UV-A (320–400 nm), penetrates water and induces direct damage to microbial DNA, forming molecular lesions that impair replication (García-Gil et al., 2022; Table 1). Additionally, cellular respiration during sunlight exposure facilitates the generation of reactive oxygen species (ROS) through electron transport processes. During this process, a fraction of free electrons interacts with oxygen, resulting in the formation of superoxide () (R.1). This superoxide is subsequently managed by superoxide dismutase (SOD) enzymes (R.2), which convert it into hydrogen peroxide (H2O2). The H2O2 is further processed by alkyl hydroperoxide reductase (Ahp) enzymes and catalases (CAT), depending on the growth phase of the microbial cell (R.3), but it can also react with internal iron via the Fenton reaction, producing hydroxyl radicals (•OH) (R.4). Additionally, ferrous iron is converted to ferric iron in this process (R.5). Both O2•− and •OH can interact with each other and with H2O2 in various reactions (R.6, R.7, and R.8), and they can cause indiscriminate damage to multiple cellular targets (R.9 and R.10). Despite this, cells might possess their own defense mechanisms to repair the damage inflicted by these reactive species (also R.9 and R.10). However, they simultaneously undergo thermal inactivation (R.11), with significant inactivation occurring at high temperatures. Previous studies indicated that temperatures above 45 °C significantly boost the inactivation process, with complete elimination observed at 55 °C after prolonged exposure (McGuigan et al., 1998). At intermediate temperatures, the contributions of radical-induced damage and thermal inactivation to cellular death are comparable. Other mechanisms can occur, such as the degradation of H2O2, including its decomposition (R.A), permeation into the cells (R.B), interactions with the cell membrane (R.C), and interactions with cellular components and debris from dead cells (R.D). These pathways represent the primary mechanisms through which externally added H2O2 is consumed ineffectively. The aforementioned processes disrupt cellular capability to replicate and ultimately results in cell death (McGuigan et al., 1998; Reed et al., 2000). These mechanisms allow SODIS to be effective even in turbid water, although high turbidity levels can shield microorganisms from UV exposure (Rai et al., 2010). However, there are variations in sensitivity to solar inactivation among different microbial strains, which can be attributed to factors such as the presence of photosensitizers and reactive oxygen quenchers (Heaselgrave et al., 2006; Boehm et al., 2012). Recent advances emphasize optimizing SODIS through the addition of safe photosensitizers and combining with mild heating to overcome these limitations and enhance pathogen reduction (McGuigan et al., 2012).
Figure 1. Mechanism of action of SODIS is primarily based on the combined effects of solar UV radiation and heat.
Table 1. Oxygen reactive species reactions—inactivation routes by radical's damage effect (García-Gil et al., 2022).
Overall, SODIS operates through a dual mechanism of UV-induced genetic damage and thermal inactivation, both of which contribute to the effective disinfection of contaminated water. However, the success of SODIS depends on optimizing factors such as water turbidity, container type, and exposure duration, all of which must be considered when implementing this technology in different environments.
3 Enhancement of SODIS
More recently, the possibility of introducing chemical and mechanical enhancers to speed up and/or inactivate a greater range of pathogenic microorganisms has been evaluated. Fisher et al. (2008) attempted to improve the technique of solar disinfection of E. coli by introducing different additives to the contaminated water (e.g., H2O2, lemon juice, and copper metal or aqueous copper). These additives were intended to enhance microorganism inactivation rates and improve solar disinfection, especially under cloudy conditions. Their findings showed that these additives did indeed increase the inactivation rate of E. coli. However, some additives had limitations: for instance, while H2O2 is generally safe, its interaction with stabilizers in solutions could pose problems. Additionally, the effectiveness of ascorbate as an additive decreased if added before reaching peak sunlight.
Riboflavin (Figure 2A), also known as vitamin B2, is a water-soluble compound (7,8-dimethyl-10-ribityl-isoalloxazine) found in foods such as milk, meat, fish, and certain vegetables and fruits. It plays a crucial role in redox reactions within aerobic cells and is known for its protective effects against cancer and cardiovascular diseases (Powers, 2003). Riboflavin is reported by FDA as Generally Regarded as Safe (GRAS), so it does not pose a hazard to the public (FDA, 2006). Its efficacy and reaction mechanisms of inactivating and damaging mammalian cells, bacteriophage, bacteria, DNA and RNA have been assessed by several studies. Hoffmann and Meneghini (1979) reported that when riboflavin and tryptophan are exposed to near-UV light, H2O2 is produced, which is toxic and responsible for the breakage of dsDNA. When riboflavin is excited, oxygen reactive species (ROS) are induced, e.g., hydrogen peroxide and singlet oxygen (Ruane et al., 2004; Besaratinia et al., 2007; Cardo et al., 2006, 2007; Lin et al., 2006; Martins et al., 2008; Silva et al., 2019). It is well established that riboflavin plays a crucial role in metabolic processes as a precursor of essential coenzymes, such as flavin adenine mononucleotide (FMN) and flavin adenine dinucleotide (FAD), which are vital for numerous redox reactions in aerobic cells (Silva et al., 2019; Reddy et al., 2008; Steindal et al., 2008). However, few studies have assessed the effectiveness of riboflavin in conjunction with solar irradiation in inactivating water-borne pathogenic viruses in water. Riboflavin is used for the treatment of keratoconus, by utilizing UV-A with riboflavin to stop the progression of the keratoconus and enhance visualization (Wollensak et al., 2003). In addition, this type of treatment is simple and cheap, making it suitable for use in poor and less developed countries. A machine called Mirasol™ PRT (CaridianBCT, USA, Figure 2B) inactivates pathogens by employing UV-A with riboflavin to destroy their nucleic acids (Goodrich et al., 2006). The use of riboflavin combined with ultraviolet (UV) light for the treatment of platelets and plasma, through the Mirasol PRT system, approved for commercial use in Europe at the end of 2007 (Chatterjee et al., 2016; Ware et al., 2018). This system leverages riboflavin's ability to act as a photosensitizer, selectively damaging the nucleic acids of microbes upon UV light exposure.
Figure 2. The chemical structure of riboflavin (A) and schematic design for the Mirasol treatment (B). Source: Chatterjee et al. (2016).
The use of such enhancers was applied on Acanthamoeba trophozoites and cysts (Heaselgrave and Kilvington, 2011). Riboflavin demonstrated high effectiveness against free-living protozoa, with Acanthamoeba trophozoites being more susceptible than cysts. The trophozoites were completely destroyed after 4 h of exposure to 150 W/m2, while cysts experienced a 3.5 log10 reduction after 6 h of exposure to 250 W/m2 in combination with 250 μM riboflavin. This inactivation method shows promise for providing safe drinking water worldwide, especially in situations where there is limited access to skilled labor, such as in disaster-stricken areas with destroyed sanitation systems (Gupta et al., 2007). The use of enhancers in SODIS may also prove effective in cloudy conditions, potentially reducing the time and cost required to inactivate a variety of microorganisms in water. Ultimately, this method could help reduce the spread of infectious microorganisms, contributing to a decrease in global disease transmission.
4 Inactivation of viruses using SODIS
Viruses, which differ in morphology from bacteria or protozoa, were significantly affected by solar irradiance when exposed to sunlight at an intensity of 150 W/m2 for 6 h, leading to permanent viral inactivation (Alotaibi and Heaselgrave, 2011). Solar UV radiation, particularly UVA and UVB bands, plays a critical role in viral inactivation by inducing structural damage to viral components (Wang et al., 2025; Wondrak et al., 2021). The success of SODIS depends on factors such as solar irradiance, oxygen availability, and exposure duration. Regions like the MENA area, with abundant sunlight and dry climates, offer ideal conditions for effective virus inactivation through solar-based methods. The viral capsid—primarily composed of proteins—protects the viral genome (Figure 3), but under prolonged sunlight exposure in the presence of oxygen, oxidative damage degrades capsid proteins and damages the viral genome (DNA/RNA). Free radicals, including hydrogen peroxide and singlet oxygen play a central role in viral inactivation during solar disinfection (Bosshard et al., 2010). The combined effects of UVA and oxygen result in protein oxidation and aggregation, ultimately distorting the viral structure. Thus, there are three main mechanisms to destroy viruses by SODIS (Figure 3). In Direct mechanisms, photons are absorbed directly by chromophores at the damage site (indicated by orange stars), leading to capsid protein and genome damage in viruses, and membrane-bound, cytosolic protein, and genome damage in bacteria (Kumar et al., 2004). In Endogenous Indirect mechanisms, photons excite internal sensitizers (Sens), generating photo-produced reactive intermediates (PPRI) like singlet oxygen (1O2) and hydrogen peroxide (H2O2), which cause damage at different sites. In Exogenous Indirect mechanisms, external sensitizers absorb photons and subsequently generate or transfer reactive intermediates to the target pathogen. This enhances structural and genomic disruption, particularly under low-light or turbid conditions.
Figure 3. Mechanisms of sunlight inactivation in viruses in comparison to bacteria (García-Gil et al., 2021). Green shapes represent proteins, and blue indicates sensitizers (Sens). UVB, UVA, and visible light play distinct roles in these processes.
In regions of MENA with intermittent sunlight or cloud cover, the addition of riboflavin (250 μM) has been shown to reduce the required anti-viral treatment time to less than 2 h, offering a practical solution in areas with inconsistent sunlight availability (Alotaibi and Heaselgrave, 2011). Increasing solar irradiance power can further shorten the inactivation period. For example, viruses such as coxsackievirus-B5 and poliovirus-2 can be effectively inactivated within 1–2 h under 550 W/m2 solar irradiance without additional enhancers (Heaselgrave and Kilvington, 2012).
Field studies in Upper Egypt demonstrated that SODIS-treated water supplemented with riboflavin in small household containers achieved >99% reduction in enteric viruses within 90 min, even under partially cloudy conditions (Heaselgrave and Kilvington, 2012). Similarly, in communities along the Moroccan Atlantic coast, SODIS exposure of water with high viral loads, including rotavirus and adenovirus, achieved significant viral reductions within 2 h under average solar irradiance of 480 W/m2, with reflective surfaces further enhancing inactivation efficiency (Polo et al., 2015). In East African households, SODIS applications under equatorial sunlight showed consistent reductions in pathogen indicators, suggesting its viability for enteric virus reduction under high solar exposure, which is comparable to conditions in MENA regions. Experiments under Mediterranean solar conditions, analogous to northern MENA coastal regions (Polo et al., 2015), showed that solar exposure significantly reduced hepatitis A virus (HAV) and murine norovirus (MNV-1) RNA copies after 8 h in PET bottles under natural sunlight (22–40 °C), with reductions between 0.8–1.1 log, indicating the influence of cumulative solar dose in these climates.
Despite the potential of solar disinfection (SODIS) for viral inactivation, viruses exhibit variable susceptibilities to the process. For instance, bacteriophage MS2 demonstrates notable resistance, with only a slight synergistic inactivation observed even under elevated solar irradiance (~5,580 kJ/m2) and temperatures (~59 °C; Theitler et al., 2012; Bichai et al., 2012). This resistance is attributed to MS2's robust capsid structure and its genetic regulatory role in the viral life cycle (Williams et al., 2024; Kuzmanovic et al., 2003; Harding and Schwab, 2012). This capsid, composed of 180 copies of coat proteins arranged in a T = 3 icosahedral symmetry, contributes to the durability and environmental stability of MS2 (Williams et al., 2024). Comparative studies indicated that poliovirus type 3 is significantly more sensitive to SODIS than MS2 and human adenovirus type 2 (Silverman et al., 2013). Environmental factors specific to the MENA region, such as altitude and light diffusion, play a role in viral inactivation efficiency. Studies suggested that higher light diffusion rates, influenced by ground albedo, increase viral inactivation rates. Recent genomic analyses indicate that the natural abundance of viruses infecting Synechococcus varies in coastal environments, with reduced salinity influencing viral diversity and abundance, which may affect the effectiveness of solar disinfection (Zhang et al., 2023).
Overall, in the MENA region, where viral contamination in water sources remains a public health concern, SODIS emerges as an accessible and sustainable solution for virus inactivation. Future research should focus on region-specific challenges, such as optimizing exposure times under varying climatic conditions and improving viral resistance management strategies, to enhance SODIS effectiveness across the region. This tailored approach to viral inactivation using SODIS aligns with the MENA region's need for low-cost, sustainable water treatment technologies, contributing significantly to improved public health outcomes and water security.
5 Future perspectives in MENA region
The MENA region faces significant water scarcity and contamination challenges, making affordable and sustainable water treatment technologies essential for ensuring public health and environmental sustainability. SODIS has emerged as a promising, cost-effective method to address these challenges, particularly in regions with abundant sunlight. According to UNICEF (2010) and the World Health Organization, diarrhea causes the death of 1.5 million children annually, primarily due to gastrointestinal infections from contaminated water. These infections often result in severe dehydration, leading to fatal outcomes. Misuse of antibiotics and pollution have further contributed to the rise of antibiotic-resistant pathogens. UNICEF emphasizes that 90% of diarrhea-related deaths are preventable with access to clean water and proper sanitation. In the MENA region, where water scarcity exacerbates hygiene-related diseases, SODIS represents an effective low-cost method to inactivate waterborne pathogens using sunlight. It is widely adopted in several MENA countries, offering a sustainable and environmentally friendly way to ensure safe drinking water. However, enhancements to SODIS, such as using photosensitizers like methylene blue (MB), material consideration, climatic and seasonal impacts, photocatalytic enhancements, and other innovative enhancements can play a significant role for improvements in disinfection efficiency (Cardoso-Rurr et al., 2019; Suliman et al., 2025). Moreover, integrating nanomaterials such as titanium dioxide (TiO2) and natural clays into the SODIS process has demonstrated improved disinfection through photocatalytic mechanisms (Hamdan et al., 2022; Paspaltsis et al., 2025; Suliman et al., 2025). These advancements offer promising avenues for enhancing SODIS performance in the MENA region, where climatic conditions and resource constraints necessitate innovative solutions for water treatment (Zhang et al., 2023).
5.1 Material considerations
Materials such as polypropylene (PP), polyethylene terephthalate (PET), polycarbonate (PC), and polymethyl methacrylate (PMMA) have been identified as suitable options for constructing SODIS devices due to their varying properties, which can influence the efficiency of UV radiation transmission required for disinfection. PP is a cost-effective material that, while affordable, has relatively lower durability and may not withstand prolonged exposure to harsh environmental conditions. In contrast, PET and PC offer a balance between cost and durability, making them more suitable for moderate-term applications, though they may still degrade over time under constant exposure to UV radiation and high temperatures. PMMA, on the other hand, is more expensive but stands out for its superior weather resistance, making it highly durable and capable of withstanding long-term exposure to solar radiation and extreme environmental conditions. Among these materials, PMMA exhibits the least reduction in UV transmission when the material thickness increases, which is a critical factor to ensure the efficiency of the SODIS process (García-Gil et al., 2020).
Recent advances have introduced nanocomposite coatings, such as those incorporating titanium dioxide (TiO2) and zinc oxide (ZnO) nanoparticles, which improve UV resistance, reduce microbial adhesion, and prolong device lifespan, enhancing overall disinfection efficiency (Conroy et al., 2001; Paspaltsis et al., 2025). In the arid and dusty environments characteristic of the MENA region, abrasion-resistant surface treatments have been shown to maintain UV transparency and device durability despite sand and dust exposure (Elsafi et al., 2025). Additionally, PMMA's ability to retain heat synergizes with UV radiation, boosting microbial inactivation through combined photothermal effects—an advantage in the region's high-temperature climate (Yurrita et al., 2021). Environmental sustainability concerns have also driven efforts to develop recyclable and biodegradable SODIS materials to mitigate plastic waste challenges associated with widespread device use (Borde et al., 2016).
In the MENA region, where solar radiation is intense and temperatures can be extreme, selecting the appropriate material for SODIS devices requires careful consideration of factors such as cost, material availability, and the ability to maintain structural integrity under these harsh conditions. Additionally, the choice of material impacts the exposure times required for effective disinfection, particularly for the inactivation of pathogens like bacteria, viruses, and protozoa. To assist in selecting the best material, the solar UV calculator is a valuable tool. This tool estimates the UV radiation exposure based on the specific properties of the materials used, helping to optimize the design of SODIS devices for different environmental conditions. For example, at a thickness of 0.5 mm, the required exposure times for bacterial inactivation were found to be as follows: PMMA 0.69, PET 1.52, PP 0.97, and PC 0.90 h. These calculated exposure times provide crucial insights into the material effectiveness in inactivating pathogens and highlight the importance of selecting the right material for different applications in MENA region, where climatic factors can significantly influence the efficiency of solar disinfection technologies (O'Dowd et al., 2023).
5.2 Climatic and seasonal impacts
A study by Nawmi and Rimi (2023) using the Weibull model have provided valuable insights into the factors affecting the efficiency of SODIS, particularly the role of solar radiation and seasonal variations. The Weibull model, a statistical tool for analyzing data on survival rates and failure times, was used to quantify how different environmental factors influence the disinfection process. In regions with distinct seasonal changes, such as tropical climates, the study revealed that during summer months, strong sunlight significantly enhances the disinfection process, enabling a rapid 4-log reduction in bacterial concentrations within just 3 h of exposure. This high efficiency is due to the intense solar radiation and longer daylight hours typically experienced in the summer, which accelerates the UV-induced inactivation of pathogens. However, during monsoon and winter seasons, the efficiency of SODIS was reduced due to lower solar irradiance, cloud cover, and shorter daylight hours. These factors led to the need for longer exposure times to achieve the same level of disinfection, as weaker sunlight was less effective at penetrating the water and driving the photoreaction needed to inactivate pathogens. The study emphasized the critical role of solar radiation in the success of SODIS and the variability of its performance based on seasonal changes in sunlight intensity.
In MENA region, however, seasonal variations are less pronounced compared to regions with more distinct climatic shifts. Sunlight remains relatively consistent year-round, which helps to maintain a stable level of SODIS efficiency across different seasons. Despite this advantage, the region faces unique challenges that can affect the effectiveness of SODIS. For instance, high water turbidity, a common issue in many MENA countries due to dust storms, sediment runoff, and agricultural runoff, can significantly hinder the penetration of UV radiation into the water, thereby reducing the disinfection efficiency. Additionally, the accumulation of dust and dirt on the surface of SODIS containers can block sunlight and further compromise the performance of the disinfection process (Sulaiman et al., 2014). To ensure consistent and reliable SODIS performance. It is crucial to address these challenges by improving water filtration techniques, regularly cleaning the SODIS containers, and possibly incorporating materials or coatings that minimize dust accumulation. These measures would help to maintain the high disinfection efficiency that SODIS offers, even in environments where particulate matter and other external factors could otherwise impede its effectiveness.
In addition to seasonal variations, the MENA region faces growing challenges from climate change, including increased rainfall variability, higher temperatures, and more frequent dust storms, all of which would contribute to elevated turbidity and microbial contamination in water sources (World Bank, 2021). High turbidity can significantly reduce the efficiency of SODIS by blocking UV radiation, which is essential for microbial inactivation. As a response, field-based and household-level interventions increasingly recommend using biosand filters (BSFs) as a pre-treatment step to improve water clarity before solar exposure. BSFs have been shown to effectively reduce turbidity and remove up to 98% of bacteria, making them suitable for integration with SODIS in rural and disaster-prone areas (CAWST, 2024; Wikipedia, 2024). Although specific studies on combined SODIS–BSF applications in MENA are limited, the documented benefits of BSFs provide a strong rationale for their inclusion in comprehensive water treatment strategies under climate-stressed conditions.
5.3 Photocatalytic enhancements
Cowie et al. (2020) emphasized the potential benefits of integrating Photocatalytic Water Treatment (PWT) with SODIS to enhance pathogen inactivation. Recent research emphasizes the benefits of integrating Photocatalytic Water Treatment (PWT) with SODIS to improve pathogen inactivation (Abou Zeid and Leprince-Wang, 2024). Photocatalysts such as titanium dioxide (TiO2) have the unique ability to utilize visible light, expanding the range of solar radiation that can contribute to the disinfection process. Photocatalysts like zinc oxide (ZnO) have also shown superior bacterial inactivation performance compared to TiO2 (Abou Zeid and Leprince-Wang, 2024). This makes PWT a promising solution, particularly in areas where sunlight is less intense or where sunlight conditions are suboptimal for traditional SODIS. The photocatalytic reaction can help break down contaminants and pathogens even under less-than-ideal lighting conditions, potentially reducing the exposure time required for effective water disinfection. For example, immobilized TiO2 photocatalysts used in parabolic solar reactors have demonstrated improved pathogen inactivation under varying sunlight conditions (Phiri et al., 2023). However, the practical application of this technology faces several challenges, particularly in ensuring the efficient removal of the photocatalyst from the treated water. Since TiO2 and other photocatalysts are typically suspended particles, they can be difficult to separate from the water without specialized filtration systems, raising concerns about their potential to remain in water and affect water quality. Moreover, issues related to the longevity of the photocatalyst, its reusability, and the cost of implementing such a system also need to be addressed for large-scale applications. These challenges regarding removal, durability, and cost have been widely reported in recent studies (Lonnen et al., 2005; Li et al., 2023).
In the arid MENA regions, where water scarcity is a significant concern, integrating photocatalysts with SODIS could offer a solution that not only enhances disinfection efficiency but also minimizes water wastage. Since SODIS relies on sunlight to disinfect water, the addition of photocatalysts could allow for more effective disinfection under varying sunlight conditions, reducing the need for prolonged exposure times. This would be particularly beneficial in areas where every drop of water is valuable, and efficient water reuse is essential. By enhancing pathogen inactivation while minimizing water usage, the integration of photocatalysts with SODIS could help to address both public health and water scarcity challenges in these regions, offering a more sustainable and reliable method for water purification.
5.4 Effectiveness of enhancers
Cardoso-Rurr et al. (2019) demonstrated that adding MB significantly reduces the time required for bacterial inactivation. The study revealed that MB, at its lowest concentration (50 ng/ml), achieved 99.9% inactivation of E. coli within just 60 min of sunlight exposure, compared to the traditional SODIS method, which typically requires over 3 h. Recent research confirms MB's effective photocatalytic activity under solar irradiation, supporting its rapid pathogen inactivation even in diverse water qualities. Higher MB concentrations further reduced the inactivation time to 30 min. Additionally, MB-SODIS achieved 99.9% viral inactivation (λ bacteriophage) in only 4 min. In the arid MENA climate, where sunlight is abundant, MB-SODIS can be particularly effective for providing quick and reliable disinfection solutions, especially in remote or underserved areas with limited access to conventional water treatment facilities. However, the use of MB also has limitations and precautions. Its effectiveness can be influenced by factors such as water turbidity, which may reduce the penetration of sunlight and the efficiency of MB. Furthermore, high concentrations of MB may lead to toxicity concerns, and the cost of the photosensitizer could limit its widespread adoption in resource-limited settings. Additionally, the disposal of used MB solutions needs to be managed carefully to avoid environmental contamination. Moreover, The WHO Guidelines for Drinking-water Quality (Sulaiman et al., 2014; World Health Organization (WHO), 2024b) do not list methylene blue among recommended or assessed disinfectants for potable water.
To address the limitations of MB-SODIS, several strategies can be considered. First, optimizing the concentration of MB is essential to balance effectiveness and cost. Studies should focus on determining the minimum effective concentration of MB for different water qualities and environmental conditions. This would help reduce the amount of MB required, lowering both costs and potential environmental impacts. To mitigate toxicity concerns, research could explore alternative, less toxic photosensitizers or the development of MB formulations that minimize harmful effects on aquatic ecosystems. Additionally, combining MB with other materials, such as natural coagulants or photocatalytic agents, may improve its efficiency in turbid waters while reducing the need for higher concentrations. Further studies are also needed to assess the long-term stability and environmental impact of MB, particularly regarding its degradation products. Investigating the potential reuse or recycling of MB in SODIS systems could also provide a more sustainable solution.
5.5 Innovative enhancements
Innovative enhancements in SODIS technology continue to evolve, offering the potential for more efficient and effective water purification in challenging environments. Alkhalidi et al. (2021) explored the integration of Wood's glass and Fresnel lenses in SODIS devices to improve pathogen inactivation. Building on this, recent studies have improved Wood's glass filters by applying advanced coatings that increase UV transmission while effectively blocking infrared radiation, further reducing bacterial regrowth and improving filter durability (Phiri et al., 2023). Moreover, combining Fresnel lenses with modified titanium dioxide (TiO2) photocatalysts has been shown to accelerate pathogen inactivation, even under variable sunlight conditions typical of arid regions (Li et al., 2023). Field trials in climates analogous to the MENA region have confirmed that these combined technologies can achieve pathogen removal rates exceeding 85%, demonstrating practical applicability for enhancing water quality in resource-limited settings (Phiri et al., 2023). Wood's glass filters are particularly beneficial as they allow UV radiation to pass through while blocking infrared light, which helps to prevent bacterial regrowth by reducing the thermal energy in water. These enhancements significantly improve the efficiency of SODIS process by harnessing the full potential of solar radiation while addressing key limitations such as bacterial regrowth, which can undermine disinfection efforts. In high-radiation environments typical of the MENA region, where sunlight is abundant and intense, and these technologies hold significant promise for further enhancing the efficiency and reliability of SODIS, making it a more effective solution for water purification in areas with limited access to conventional treatment methods.
Overall, while SODIS remains a highly effective and low-cost water disinfection method, integrating photosensitizers, optimizing materials, and leveraging advanced photocatalytic techniques can significantly enhance its efficiency. These enhancements, particularly when adapted to the unique environmental and climatic conditions of the MENA region, hold the potential to improve the reliability and scalability of SODIS, making it a more effective solution for addressing waterborne diseases and ensuring access to clean water in underserved areas.
6 Conclusions
SODIS has the potential to be a low-cost and practical method for improving water safety, especially in regions like MENA where water scarcity and waterborne diseases are major challenges. By utilizing the abundant solar energy in the region, SODIS could address the lack of access to safe drinking water, particularly in rural and underserved communities or under environmental disasters. The technology harnesses the combined effects of solar UV radiation and thermal heating to inactivate a wide range of pathogens, including bacteria, viruses, and protozoa. This dual mechanism could reduce the presence of microbial hazards in drinking water, without the need for chemicals, expensive equipment, or electricity, making SODIS highly suitable for low-resource settings. Despite its advantages, the success of SODIS depends on several key factors, including sunlight intensity, water turbidity, and the type of container used. Clear skies and strong sunlight are essential for achieving optimal results, while cloudy conditions can extend the time required for disinfection. The time factor can be overcome by adding enhancers, especially in conditions that block the sun's rays for a full day. SODIS has proven to be effective in reducing the incidence of waterborne diseases in various parts of the world, and its potential for the MENA region is significant. However, widespread adoption of the technology will require addressing challenges such as public awareness, education, and cultural acceptance. Community education programs and support from governments and NGOs will be essential in ensuring that SODIS is understood and embraced as a viable solution for water treatment.
Data availability statement
The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding authors.
Author contributions
MA: Writing – review & editing, Funding acquisition, Writing – original draft, Validation, Conceptualization. HA-K: Software, Methodology, Writing – review & editing, Supervision, Writing – original draft, Investigation, Conceptualization, Formal analysis, Visualization, Data curation, Resources, Project administration, Validation.
Funding
The author(s) declared that financial support was not received for this work and/or its publication.
Acknowledgments
The authors would like to thank management of Kuwait Institute for Scientific Research for its continuous support. Special thanks to colleagues and experts who provided valuable insights and suggestions that enhanced the quality of this work.
Conflict of interest
The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Generative AI statement
The author(s) declared that generative AI was not used in the creation of this manuscript.
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Abbreviations
SODIS, solar disinfection; MENA, Middle East and North Africa; DNA, deoxyribonucleic acid; RNA, ribonucleic acid; GRAS, generally regarded as safe; PET, polyethylene terephthalate; UV-A, ultraviolet-A; ROS, reactive oxygen species; H2O2, hydrogen peroxide; 1O2, singlet oxygen; , superoxide; •OH, hydroxyl radicals; UV, ultraviolet; CFU/ml, colony-forming units per milliliter; SOD, superoxide dismutase; Ahp, alkyl hydroperoxide reductase; CAT, catalase; FMN, flavin adenine mononucleotide; FAD, flavin adenine dinucleotide; W/m2, watts per square meter; PPRI, photo-produced reactive intermediates; UNICEF, United Nations International Children's Emergency Fund; MB, methylene blue; TiO2, titanium dioxide; PP, polypropylene; PC, polycarbonate; PMMA, polymethyl methacrylate; ROS, reactive oxygens species; ZnO, zinc oxide; PWT, photocatalytic water treatment.
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Keywords: encapsulated microorganisms, hydrogen peroxide, pathogen inactivation, SODIS, solar disinfection
Citation: Alotaibi M and Al-Khalaifah H (2026) Potential of solar water disinfection (SODIS) for pathogen control during water scarcity crisis. Front. Water 7:1679793. doi: 10.3389/frwa.2025.1679793
Received: 05 August 2025; Revised: 19 December 2025;
Accepted: 29 December 2025; Published: 12 February 2026.
Edited by:
Ashish Kumar Singh, Center of Innovative and Applied Bioprocessing (CIAB), IndiaReviewed by:
R. Naresh Kumar, Birla Institute of Technology, Mesra, IndiaYanjiao Gao, Liaoning University of Technology, China
Copyright © 2026 Alotaibi and Al-Khalaifah. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Mohammad Alotaibi, bWFvdGFpYmlAa2lzci5lZHUua3c=; Hanan Al-Khalaifah, aGtoYWxpZmFAa2lzci5lZHUua3c=