Introduction
The rapid pace of industrialization and population growth has led to the deterioration of both water quality and availability (Sarker et al., 2021). Water sources are increasingly being contaminated by industrial discharges, agricultural runoff, and untreated sewage. Such pollution introduces hazardous substances that make water unsafe for the aquatic ecosystem and human use. This, in turn, adversely affects the aquatic environment like rivers and oceans, which are essential for sustaining life, and consequently poses risks to human health (Bhattarai and Bhasin, 2022). Industrial wastewater is particularly hazardous due to its high concentration of toxins that can seep into groundwater and nearby water bodies. Many areas of groundwater and surface water have been polluted with heavy metals and persistent organic pollutants, thus triggering health concerns (Kristanti et al., 2021; Mawari et al., 2022). If used for irrigation, this contaminated water can degrade crop quality and introduce harmful chemicals into the food chain, ultimately contributing to diseases such as lung cancer, weakened immune system, and liver and kidney damage (Musa Khan, Bano and Ishaq Khan, 2022).
Access to clean and safe drinking water is a fundamental human need and serves as a critical component of public health. Despite global advancements, approximately 1.1 million people still lack access to safe drinking water. In many developing countries, communities rely on surface water, groundwater (e.g., wells), and harvested rainwater—sources that are often susceptible to contamination by pathogenic microorganisms such as Escherichia coli and Pseudomonas spp. These pathogens contribute significantly to the global burden of waterborne diseases. According to the World Health Organization (WHO), over 1 million deaths annually are attributed to diarrheal illnesses linked to the consumption of contaminated water and seafood. Besides harmful microbes, toxic heavy metals like lead (Pb), nickel (Ni), cadmium (Cd), and chromium (Cr(VI)) also increase public health risks, contributing to serious health problems. For example, in Eluru, India, an outbreak of neurological symptoms in over 500 residents was linked to elevated levels of Pb and Ni in the water, highlighting the acute danger posed by metal contamination (Atikpo et al., 2021). Prolonged mining operations in Kabwe, Zambia had caused elevated Pb concentrations in drinking water, contributing to developmental delays and neurological disorders among children (Siame et al., 2023). Research conducted in Lahore, Pakistan identified elevated levels of Pb and Cd in groundwater, leading to cancer risks and skin health issues (Iqbal et al., 2024). Furthermore, excessive Cr(VI) in drinking water posed carcinogenic risks to the local population in Badagry, Nigeria (Oloruntoba, Wada and Adejumo, 2022).
The lack of safe drinking water remains a leading cause of waterborne disease outbreaks worldwide. To address this challenge, effective drinking water treatment technologies tailored to local environmental and infrastructural conditions are essential. This paper explores various potential drinking water treatment methods aimed at improving water quality and ensuring reliable access to safe, potable water, ultimately safeguarding human health and improving quality of life.
Methodology
Relevant literature published between 2020 and 2025 was systematically identified through searches in Scopus and Web of Science. The search strategy used combinations of the following keywords: “Disinfection By-products”, “Drinking Water Treatment”, “Nanomaterials”, “Drinking Water”, “Emerging Pollutants”, and “Water Purification”. Studies were included if they were peer-reviewed and addressed drinking water purification methods or emerging environmental challenges, particularly those related to disinfection by-products, nanomaterials, or emerging pollutants. Publications falling outside the defined timeframe or lacking direct relevance to drinking water treatment were excluded from the review. Data from eligible studies were extracted on treatment techniques, targeted contaminants, and performance outcomes. A narrative synthesis was then conducted to integrate and compare the findings, and to organize studies by treatment category (e.g., chemical disinfection, adsorption, membrane filtration, nanomaterial-based technologies).
Methods of Water Treatment
Various water treatment methods have been employed to improve water quality and reduce health risks associated with contaminated sources in developing countries. Common water treatment methods include chlorination, flocculation, filtration, and biological filtration (Mazhar et al., 2020; Rahim, Sunarsih and Budiati, 2024).
Chlorination
Chlorination remains one of the most widely implemented methods for disinfecting drinking water treatment systems. This process commonly utilizes sodium hypochlorite (NaClO) as the active disinfectant agent (Kesar and Bhatti, 2022). NaClO acts by disrupting the structural integrity of microbial cell membranes and denaturing essential proteins, ultimately causing microbial cell death (Nizer, Inkovskiy and Overhage, 2020). The efficiency of this disinfection method extends across a broad spectrum of pathogenic microorganisms, including viruses; under controlled conditions (pH 7.0–7.2, chlorine dose 0.2–3 mg/L, and temperature around 5°C), all viruses examined demonstrated hypersensitivity or high sensitivity to chlorination, with complete inactivation achievable at a CT value of 10 mg·min/L (Kong et al., 2021). Recent advancements in molecular methods, such as high-throughput amplicon sequencing, have allowed for more detailed assessments of chlorination efficiency by tracking microbial community changes before and after treatment (Pinar-Méndez et al., 2022). These methods allow for detailed profiling of microbial communities before and after treatment, thereby providing insights into residual microbial populations, resistance patterns, and treatment optimization. Studies employing these tools have highlighted not only the effectiveness of chlorination but also the potential for selection of chlorine-resistant taxa under suboptimal dosing conditions (Hwang et al., 2012).
Previous research has examined how microbial communities change in drinking water systems following chlorination and found that certain microbial groups can survive the disinfection process. These chlorine-resistant taxa tend to persist particularly when chlorine levels are inconsistently maintained at effective concentrations. This finding supports the concern that inadequate or suboptimal chlorination may not only fail to eliminate all pathogens but also unintentionally favor the survival and proliferation of resistant organisms, thus posing a risk to water safety and public health. Despite its proven efficacy, chlorination must be carefully managed to avoid the formation of harmful by-products and ensure optimal disinfection performance. Compounds such as trihalomethanes and haloacetic acids, which can form during chlorination, have been associated with adverse health effects. Notably, much of the past concerns have focused on their potential carcinogenicity (Mazhar et al., 2020).
Flocculation
The flocculation process is typically applied to enhance the removal of suspended solids. Flocculation involves adding agents—such as polyaluminum chloride—to wastewater to aggregate fine particles into larger clusters, or flocs, which can be more easily removed through sedimentation or filtration (Esteki et al., 2024). Traditionally, a wide range of flocculants has been employed in water treatment processes, primarily including inorganic salts like aluminum sulfate (alum) and organic polymers like polyacrylamide (Ghernaout, 2020; Maćczak, Kaczmarek and Ziegler-Borowska, 2020). These flocculants facilitate the aggregation of suspended particles into larger flocs, thus enhancing sedimentation and removal efficiency. Inorganic flocculants are valued for their cost-effectiveness and strong charge neutralization capacity, while organic polymers are recognized for producing larger, more stable flocs and functioning effectively at lower dosages (Maćczak, Kaczmarek and Ziegler-Borowska, 2020).
Recent innovations include magnetic flocculation, which uses magnetic particles or composite materials to enhance the flocculation process. When exposed to a magnetic field, these materials facilitate rapid sedimentation, making the treatment process more efficient. Magnetic flocculation also offers the benefit of lower chemical usage while improving the removal of pollutants from water (Hu et al., 2024). Previous study demonstrated an effective method for removing microplastics from water using magnetic nano-Fe3O4 particles (Shi et al., 2022). These nanoparticles bind to common plastics like polyethylene (PE) and polystyrene (PS), allowing for easy removal with a magnet. The technique achieved over 80% removal efficiency in both pure and environmental water samples, showing strong potential for treating microplastic contamination in drinking water. Researchers at RMIT University developed a magnetic nanomaterial featuring a nano-pillar structure composed of carbon-coated iron oxide (CC-FeO) integrated with two-dimensional metal–organic frameworks (2D-MOFs) (Haris et al., 2023). This innovative adsorbent effectively attracts and removes microplastics and dissolved pollutants (i.e., methylene blue) from water. The process achieved 100% removal of microplastics and methylene blue simultaneously within an hour, offering a sustainable and efficient solution for improving drinking water quality.
Filtration
Filtration technologies have significantly evolved by incorporating advanced materials and hybrid systems to address environmental challenges and enhance pollutant removal. Among the most popular systems are ceramic microfiltration membranes, known for their durability and resistance to extreme conditions. However, these systems are still prone to fouling, which necessitates regular cleaning and pretreatment (Haris et al., 2023). Carbon-based nanomaterials, such as carbon nanotubes and graphene, have emerged as powerful filtration media due to their superior adsorption capacity and antimicrobial properties. These materials are especially effective in removing heavy metals and pathogens from water (Chadha et al., 2022). A recent study introduced a regeneratable graphene-based water filter comprising of graphene oxide (GO) and claisen graphene (CG) in a 90:10 weight ratio (Schmidt, Dou and Sydlik, 2023). This advanced filter exhibited significantly higher heavy metal adsorption capacity than conventional activated charcoal. It achieved removal efficiencies of 90% for Pb, 70% for Cd, and 90% for mercury (Hg) in contaminated water. More importantly, the filter can be regenerated using hot water (80°C) or vinegar while maintaining its performance over multiple reuse cycles. This reusable design presents a sustainable and cost-effective approach to household water purification.
Biological Filtration
Biological filtration is a sustainable and cost-effective method for removing contaminants from drinking water. It relies on the formation of microbial biofilms on filter media such as sand or granular activated carbon. These biofilms support microbial communities that actively degrade organic pollutants, reduce nutrient loads, and eliminate pathogens (Bai, Dinkla and Muyzer, 2022). Biological filtration is used to remove ammonium from water through the nitrification process, which depends on factors like water quality and filtration parameters. A pilot study at a drinking water treatment plant used nitrifying biofilters to assess how filtration rate affects nitrification efficiency. Under optimal conditions, biofilm formation took approximately 70 days in water with ~1 mg/L of ammonium (NH4+), high dissolved oxygen (>9 mg/L), a filtration rate under 1 m/h, temperatures above 12°C, and pH between 7.8–8.0. Once biofilms were fully developed, the system achieved over 95% NH4+ removal across filtration rates from 0.5 to 8.4 m/h, even as ammonium concentrations increased (1–2.5 mg/L) and temperatures dropped (13 to 7°C) (Dragić, Drljača and Zoric, 2024). A summary of drinking water treatment methods and removal rates is presented in Table 1.
Table 1
Drinking water treatment methods and removal rates.
| METHOD | POLLUTANTS | REMOVAL EFFICIENCY | REFERENCE |
|---|---|---|---|
| Chlorination | Viruses | Complete inactivation at CT value of 10 mg·min/L | (Kong et al., 2021) |
| Flocculation (magnetic Fe3O4) | Microplastics (PE, PS) | > 80% removal in lab & environmental samples | (Shi et al., 2022) |
| Flocculation (CC-FeO + 2DMOF nanocomposite) | Microplastics & methylene blue dye | ≈ 100% removal within 1 h | (Haris et al., 2023) |
| Filtration (GO/CG graphene filter) | Pb, Cd, Hg | Pb 90%; Cd 70%; Hg 90% | (Schmidt, et al., 2023) |
| Biological filtration (nitrifying biofilter) | NH4+ | > 95% across 0.5 – 8.4 m h–¹ flow rates | (Dragić, et al., 2024) |
Adsorption
Maximizing the performance of adsorption processes largely depends on the careful selection of appropriate adsorbents. An effective adsorbent is generally characterized by a high adsorption capacity, rapid adsorption kinetics, ease of separation or recovery from aqueous media, as well as high porosity with small pore diameters, which enhance surface area availability and consequently improve adsorption efficiency (Abegunde et al., 2020). A wide range of materials has been employed as adsorbents for diverse applications, including water purification, catalysis, desiccation, and sensing. Among the most widely investigated adsorbents are activated carbon, cellulose, natural minerals, silica, biopolymers, and nanomaterials.
Adsorbents such as silica, zeolites, and activated carbon are particularly attractive owing to their low cost, natural abundance, and excellent adsorption performance (Zhu et al., 2021). Among them, activated carbon (AC) is the most widely utilized adsorbent for water decontamination, primarily due to its exceptionally high surface area and strong affinity toward heavy metals and dye molecules. Various forms of activated carbon, including granular activated carbon, powdered activated carbon, and activated carbon cloth, have been employed for pollutant removal from aqueous systems. Similarly, zeolites—typically aluminosilicates or aluminophosphates—also demonstrate notable adsorption capacity for heavy metals. Natural zeolites, in particular, are regarded as one of the most economical alternatives among commercially available adsorbents, owing to both their cost-effectiveness and inherently high porosity, which further enhances their adsorption potential (Chmielewská et al., 2019). Silica-based materials have gained significant attention as promising sorbents, offering a broad range of applications. Their inherently large surface area, along with uniform and evenly distributed pores, makes them highly effective. Functionalized silica, in particular, has been widely applied as an efficient adsorbent for the removal of heavy metal ions and other hazardous contaminants (Chua et al., 2021; Da’na et al., 2017).
Table 2 presents the performance of silica, zeolite, and AC in reducing various water pollutants, with results compared against the permissible limits for drinking water. The data indicate that the effectiveness of each adsorbent varies considerably depending on the type of pollutant. For ammonium, zeolite achieved the best performance, reducing the concentration from 5.50 mg/L to 1.50 mg/L, which exactly meets the permissible limit. In contrast, silica and AC showed limited efficiency, with final concentrations still exceeding the acceptable threshold, highlighting zeolite’s strong ion-exchange capacity for ammonium removal. For iron, silica significantly outperformed the other adsorbents by reducing the concentration to 0.10 mg/L, well below the permissible limit of 0.3 mg/L. This suggests that silica, with its high surface reactivity, has a strong affinity for iron ions, whereas zeolite and AC were less effective. In the case of phosphate, AC proved to be the superior adsorbent, lowering the concentration from 4.0 mg/L to 0.25 mg/L, while zeolite also achieved substantial reduction (1.20 mg/L). Silica, however, demonstrated only moderate removal (2.80 mg/L), indicating that surface functionalization may be critical for phosphate adsorption.
Table 2
Adsorption performance of silica, zeolite, and AC in reducing pollutant concentrations. (Malekmohammadi et al., 2016).
| Pollutant | Ci (mg/L) | SILICA ADSORBENT | ZEOLITE ADSORBENT | ACTIVATED CARBON ADSORBENT | DRINKING WATER STANDARD (mg/L) |
|---|---|---|---|---|---|
| Cout (mg/L) | Cout(mg/L) | Cout (mg/L) | |||
| Ammonium | 5.50 | 4.70 | 1.50 | 3.50 | 1.50 |
| Iron | 0.55 | 0.10 | 0.50 | 0.35 | 0.3 |
| Phosphate | 4.00 | 2.80 | 1.20 | 0.25 | N/A |
| COD | 200 | 70.0 | 180 | 21.00 | 0 |
| Turbidity* | 100* | 81.0* | N/A | 9.7* | 5* |
[i] Remarks: (*) is in NTU (nephelometric turbidity unit), N/A is no data available, Ci is initial concentration, Cout is final concentration.
With respect to organic pollutants, as measured by COD, AC exhibited a remarkable reduction from 200 mg/L to 21.0 mg/L, far surpassing the performance of silica (70.0 mg/L) and zeolite (180 mg/L). This underscores the well-known advantage of AC’s high surface area and microporous structure in adsorbing a broad range of organic molecules. A similar trend was observed for turbidity, where AC reduced values to 9.7 NTU, approaching but not attaining the permissible limit of 5 NTU, whereas silica achieved only partial removal (81.0 NTU) and no data were reported for zeolite.
Overall, the data highlight that no single adsorbent is universally effective for all pollutants. Zeolite is highly effective for ammonium due to its ion-exchange capacity, silica is particularly suitable for iron removal, and AC demonstrates superior performance for phosphate, COD, and turbidity reduction. Nevertheless, it is also evident that neither silica nor AC consistently achieved permissible levels for ammonium and turbidity, indicating inherent limitations. These findings suggest that integrated or hybrid adsorbent systems may be required to meet stringent drinking water standards across multiple pollutant categories, rather than relying on a single material.
While silica, zeolite, and AC each demonstrate specific strengths in pollutant removal, the data also reveal significant limitations when applied individually. For example, silica, although highly effective for iron removal, performs poorly for phosphate and turbidity reduction. Zeolite shows strong affinity for ammonium but provides only moderate removal for other pollutants. AC, despite its superior performance for COD, phosphate, and turbidity, does not consistently achieve permissible levels for ammonium and turbidity. These inconsistencies suggest that the adsorption efficiency of conventional adsorbents is pollutant-specific and may not be sufficient to meet comprehensive drinking water standards when used alone.
This gap points to the need for hybrid or composite adsorbent systems that combine the complementary properties of different materials. For instance, coupling AC with zeolite or silica could simultaneously enhance organic matter removal while improving ion-exchange capacity for ammonium and iron. Moreover, the functionalization of adsorbents with tailored surface groups or nanomaterials offers a promising direction to improve selectivity and adsorption kinetics. Recent studies on nanocomposites, biochar-based hybrids, and functionalized mesoporous silica have shown enhanced performance due to increased surface reactivity and synergistic effects between components.
Future research should therefore focus on developing cost-effective, sustainable, and multifunctional adsorbents that integrate high porosity, selective ion-exchange capacity, and broad-spectrum adsorption ability. Such advances would not only overcome the limitations observed in traditional adsorbents but also provide more reliable solutions for meeting stringent global water quality standards.
In summary, silica, zeolite, and AC each exhibit distinct advantages as adsorbents for water treatment, with their effectiveness strongly influenced by pollutant type. Zeolite demonstrates superior ammonium removal through ion-exchange mechanisms, silica shows high efficiency for iron due to its surface affinity, and AC remains the most versatile option, particularly for phosphate, COD, and turbidity reduction. However, none of these adsorbents alone is capable of achieving comprehensive pollutant removal at levels consistently below permissible drinking water standards. This limitation underscores the necessity of moving beyond conventional single-material systems toward hybrid and functionalized adsorbents. Integrating the complementary properties of these materials, particularly through composite structures or nanomaterial modification, holds great promise for developing cost-effective, sustainable, and multifunctional sorbents. Such approaches are likely to play a pivotal role in advancing water purification technologies and ensuring compliance with increasingly stringent environmental regulations.
Emerging Technologies and Nanotechnology-based Approaches
Nanotechnology has emerged as a rapidly developing field in drinking water treatment, offering significant potential to enhance existing production processes. Among various nanomaterials, titanium dioxide (TiO2) and silver (Ag) nanoparticles have attracted considerable attention due to their demonstrated antimicrobial properties and broad-spectrum effectiveness against pathogens. Despite this potential, the application of nanoparticle (NP)-based technologies in drinking water production remains limited compared to their wider use in other fields such as environmental remediation, wastewater treatment, and the agri-food sector, including food packaging. Nevertheless, future advancements are expected to expand the integration of nanomaterials, particularly nanoparticles, into advanced water treatment processes. In contemporary drinking water treatment, nanotechnology can play a pivotal role in pathogen disinfection, heavy metal removal, point-of-use purification, and the reduction of natural organic matter (NOM). Current applications of nanoparticles in this sector predominantly focus on disinfection, adsorption-based heavy metal removal, nanofiltration, and the elimination or detoxification of organic contaminants, highlighting their versatility as multifunctional treatment agents.
Nanomaterials, particularly NPs such as ZnO, CuO, TiO2, and Mn3O4, have been shown to exhibit strong adsorption capacities for arsenic in drinking water treatment (Arora, 2021). Despite their promising laboratory-scale results, large-scale commercialization remains limited due to the high production costs of these nanomaterials, which likely explains the absence of widely implemented nano-based adsorption columns for arsenic removal in groundwater and surface water systems. This gap is increasingly critical as global drinking water demand continues to rise, requiring treatment technologies that are not only highly efficient but also economically viable and operationally simple. The potential of tetravalent manganese feroxyhyte nanoparticles for As(V) removal has been demonstrated, where the polymerization of metal-oxyhydroxyl chains increased the availability of adsorption sites and enhanced arsenic uptake (Pinakidou et al., 2016). Their experiments reported removal efficiencies ranging between 2.1% and 2.5%. Other heavy metals such as Pb, Cd, and Ni have also been shown to be effectively adsorbed using CeO2-, Fe-, and Ag-based nanoparticles (Bettini et al., 2014), reinforcing the broad applicability of nanoscale materials.
Nevertheless, the translation of such laboratory findings to real drinking water systems remains challenging. Nano-based adsorption may underperform under real water conditions due to the presence of competing ions and complex water chemistry, which can substantially reduce adsorption efficiency, as highlighted by Simeonidis et al., 2015. Despite these challenges, their work with magnetite nanoparticles showed promise: Cr(VI) concentrations of 50 µg L–¹ were reduced to below 10 µg L–¹ within 5 hours, even at pH > 7.5, with an adsorption capacity of 2 µg mg–¹. Importantly, the nanoparticles were synthesized from inexpensive iron salts (FeSO4 and Fe2(SO4)3), yielding a treatment cost of approximately 3.5 EUR/kg (dry basis) and an estimated annual cost of 5 EUR per inhabitant, demonstrating the potential for low-cost scalability.
Taken together, these findings underscore both the promise and the limitations of nanoparticle-based adsorption in drinking water treatment. While nanomaterials provide superior adsorption capacities and selectivity for contaminants such as As, Pb, Cd, Ni, and Cr, issues related to high production costs, incomplete performance data, and reduced efficiency under realistic water chemistries remain major barriers to commercialization. Future research must therefore focus on cost reduction strategies, long-term stability assessments, and hybrid systems that integrate nanoparticles with conventional adsorbents to achieve both technical efficiency and economic feasibility for large-scale drinking water applications.
Nanomaterials, particularly NPs such as ZnO, CuO, TiO2, and Mn3O4, have been shown to exhibit strong adsorption capacities for arsenic in drinking water treatment. Nevertheless, their large-scale application remains constrained by high production costs and uncertainties regarding long-term stability and environmental safety. Future research is therefore expected to focus on the development of green synthesis routes, strategies to improve regeneration and reusability, as well as comprehensive risk and safety assessments, in order to facilitate sustainable and practical implementation of NP-based technologies in real water treatment systems.
Challenges in Drinking Water Treatment
Modern water treatment systems face numerous significant challenges that compromise their effectiveness and pose serious risks to public health and the environment. These challenges include the presence of emerging contaminants in water systems, temperature variations driven by climate change and urban heat islands, the generation of toxic sludge during coagulation processes, and the global impact of climate change on water resources.
Emerging Contaminants in Water Systems
One of the primary concerns in modern water treatment is the increasing presence of emerging contaminants, including pharmaceuticals, pesticides, and microplastics (Nadia Morin-Crini et al., 2022). These pollutants are not traditionally regulated and have only recently been recognized for their potential harm to human health and ecosystems. They enter water sources through multiple pathways, including untreated or partially treated wastewater, agricultural runoff containing chemical residues, and industrial discharges that release synthetic compounds. Due to their complex chemical structures and persistence in the environment, these substances are often resistant to removal by conventional water treatment systems, which are not designed to target such micro-pollutants (Nzereogu et al., 2024). As a result, they can remain in treated water, subsequently raising concerns about long-term exposure and environmental accumulation. Addressing this issue requires advanced treatment technologies, such as activated carbon adsorption, advanced oxidation processes, and membrane filtration, along with updated regulations and monitoring strategies (Shahid et al., 2021).
Temperature Variation Driven by Climate Change and Urban Heat
Another major challenge in water treatment is the impact of temperature variations, which directly influence both the treatment process and the distribution of drinking water (Mishra, 2023). Rising temperatures, often driven by climate change and urban heat island effects, can significantly affect the chemical and biological stability of treated water. One of the most critical consequences is the accelerated decay of chlorine, a common disinfectant used to eliminate harmful pathogens (Calero Preciado et al., 2021). As chlorine degrades more rapidly at higher temperatures, its residual concentration in the water distribution system diminishes, thereby reducing disinfection efficiency and increasing the risk of microbial contamination. In addition to chemical degradation, elevated temperatures also create favorable conditions for microbial regrowth and biofilm formation within pipes and storage tanks (Agudelo-Vera et al., 2020; Calero Preciado et al., 2021). Biofilms can harbor pathogens and protect them from disinfectants, posing a serious threat to water quality and public health, especially at the point of use. These temperature-related issues are particularly concerning in regions experiencing frequent heatwaves or lacking climate-resilient infrastructure. To address these risks, it is essential to develop and implement responsive system designs (Carbonari et al., 2025), such as temperature-adaptive disinfection strategies, improved pipe materials, and real-time monitoring technologies. Furthermore, robust regulatory frameworks and proactive management practices are needed to ensure the delivery of safe drinking water under changing climate conditions.
Generation of Toxic Sludge during Coagulation Processes
The generation of toxic sludge during coagulation processes remains a significant environmental and operational concern in water treatment. Traditional coagulants like aluminum and iron salts are effective in removing turbidity and suspended solids but produce large volumes of non-biodegradable sludge that often contains residual metals, ultimately posing disposal challenges especially in regions with limited infrastructure (Patchaiyappan and Devipriya, 2021). Improper sludge management can result in heavy metal leaching, environmental contamination, and additional health risks. Moreover, such sludge can hinder biological treatment processes and increase operating costs. In response, biocoagulants and bioflocculants derived from natural sources like plant extracts, microbial metabolites, and marine organisms have gained attention as eco-friendly alternatives. These materials offer benefits such as biodegradability, lower toxicity, and potential reuse of the resulting sludge as biofertilizer (Badawi, Salama and Mostafa, 2023). However, limitations like raw material inconsistency, seasonal variability, limited shelf life, and scalability issues currently restrict their widespread application (Kurniawan et al., 2020). To address these constraints, ongoing research is focused on optimizing extraction and production methods, improving coagulation efficiency, and integrating bio-based solutions into existing treatment frameworks.
Global Impact of Climate Change on Water Resources
Climate change significantly impacts global water resources by altering rainfall patterns, increasing the frequency of droughts, and intensifying extreme weather events, all of which compromise water availability and quality. These changes are particularly detrimental to developing countries, where limited water treatment infrastructure heightens vulnerability to waterborne diseases such as cholera and typhoid. For instance, in Malawi, the combination of tropical storms and heavy rainfall in 2022 led to the country’s largest cholera outbreak, with over 36,000 cases and 1,200 deaths reported by early 2023. Similarly, in Kenya, prolonged drought conditions have been linked to increased cholera cases due to compromised sanitation and water scarcity (Alam, 2023). To address these challenges, experts advocate for a holistic approach to sustainable water management under climate stress. This includes the integration of advanced technologies, resilient infrastructure, community engagement, and effective water governance. Nature-based solutions, such as constructed wetlands and rainwater harvesting systems, have shown promise in enhancing water resilience (Barman, Rajak and Jha, 2024). Additionally, initiatives like Odisha’s adaptive governance framework aim to foster climate-resilient development by strengthening climate-risk management and promoting community-driven adaptation strategies (Meher, 2024). Implementing such comprehensive strategies is crucial for safeguarding water resources and public health amidst ongoing climate change.
Future Research Directions
Future research on drinking water purification must go beyond incremental technological advances and embrace a more systemic, multidisciplinary perspective. One critical direction involves the integration of circular economy principles into water treatment research. Conventional treatment processes typically focus on removing contaminants to achieve compliance with regulatory standards, but they often overlook opportunities for resource recovery. Future technologies should therefore not only purify water but also reclaim valuable materials such as phosphorus, nitrogen, and trace metals. For example, phosphorus recovery from wastewater streams could support sustainable fertilizer production, while selective adsorption and nanomaterial-based filtration systems may allow the extraction of rare earth elements from industrial effluents. Embedding such resource recovery strategies into treatment design would simultaneously improve environmental sustainability, reduce waste generation, and create new economic opportunities.
A second research priority lies in the development of decentralized and point-of-use treatment systems, particularly in low-resource and rural settings where centralized treatment infrastructure is either absent or unreliable. The future of global water security will increasingly depend on portable, adaptable, and cost-effective systems capable of providing safe drinking water during emergencies, climate-related disasters, or in remote communities. Solar-driven disinfection units, compact adsorption filters using biochar or nanocomposites, and membrane-based kits represent promising approaches. These systems must be designed with affordability, robustness, and ease of maintenance in mind, ensuring that vulnerable populations are not excluded from technological benefits.
Another promising area of research is the integration of renewable energy with water treatment technologies. The energy-intensive nature of many advanced purification techniques, including membrane filtration and advanced oxidation processes, raises concerns about carbon footprints and operational costs. Coupling these systems with renewable energy sources such as solar, wind, or biomass could significantly reduce environmental impacts while enhancing resilience in off-grid or energy-scarce regions. Recent work in solar photocatalysis, particularly with TiO2-based nanomaterials, demonstrates the feasibility of harnessing solar energy for pathogen inactivation and degradation of organic pollutants. Future studies should emphasize hybrid systems that co-optimize energy and water treatment efficiencies, ultimately contributing to the dual goals of climate change mitigation and water security.
In parallel, the concept of digital twins and smart water infrastructure is expected to transform the water sector. Digital twin technologies, which create dynamic, virtual replicas of physical systems, can simulate treatment performance under varying environmental conditions and contaminant loads. By integrating real-time monitoring data with artificial intelligence, digital twins could predict system failures, optimize chemical dosing, and improve resilience against shocks such as sudden pollution events or heatwaves. Such predictive systems could be particularly transformative for utilities operating under resource constraints, enabling preventive maintenance and adaptive responses at lower cost.
The future of drinking water treatment research must also confront socioeconomic and equity considerations, which remain underexplored in the technical literature. While high-income regions experiment with sophisticated nanotechnology and smart infrastructure, large portions of the global population still lack access to basic clean water. Future studies should therefore examine affordability, accessibility, and community-level adaptability of emerging technologies. Participatory approaches, where local populations are actively engaged in the co-design and testing of technologies, can enhance cultural acceptance and ensure that innovations address real-world needs. Moreover, policies must be aligned with research to prevent technological disparities from widening global inequities in access to safe drinking water.
Emerging contaminants, particularly pharmaceuticals, endocrine-disrupting chemicals, and microplastics, pose another domain for intensified research. While many current studies demonstrate removal efficiencies under laboratory conditions, their persistence in real water matrices often undermines treatment success. Future investigations must prioritize multifunctional hybrid technologies that combine adsorption, advanced oxidation, and membrane separation in integrated systems. Hybrid bio-nano composites, catalytic membranes, and bioelectrochemical systems are promising directions that could address the complex chemical diversity of these contaminants more effectively than single-method approaches.
A further critical consideration is the long-term sustainability, safety, and environmental risk assessment of new technologies. Nanomaterials, for example, offer extraordinary efficiency for pollutant removal, yet their potential release into aquatic systems raises concerns about ecotoxicity and human health impacts. Systematic studies on life cycle assessment, regeneration potential, and safe disposal methods of emerging materials are urgently required. Green synthesis methods using plant extracts, microbial processes, or biopolymers offer a potential pathway to safer nanomaterial production, but scalability and cost remain significant hurdles. Addressing these gaps will ensure that future technologies are not only efficient but also environmentally and socially responsible.
Another critical dimension for future research is the incorporation of climate resilience into water purification technologies. Climate change not only alters the quantity and distribution of water resources but also affects their quality through rising temperatures, flooding, salinity intrusion, and the increased mobilization of contaminants. These conditions can undermine the stability of traditional treatment processes and accelerate the decay of disinfectants. Future treatment systems should therefore be designed with adaptive capabilities that can perform reliably under fluctuating environmental conditions. For example, modular purification units capable of withstanding temperature extremes, or systems that combine physical, chemical, and biological mechanisms in a flexible architecture, may provide resilience in the face of climate variability. By embedding climate adaptation into technology design, research can ensure that drinking water purification systems remain robust and effective in a rapidly changing global environment.
Equally important is the recognition that the future of water purification cannot be solved by engineering and materials science alone. Instead, interdisciplinary collaboration will be essential to bridge technical innovation with social, environmental, and economic priorities. Environmental scientists, engineers, data specialists, public health experts, and social scientists must work together to design systems that not only meet technical performance criteria but also align with community needs, governance structures, and long-term sustainability. Such cross-disciplinary approaches can also accelerate the translation of laboratory findings into field applications by ensuring that the social acceptability and policy implications of new technologies are considered from the outset.
At the policy level, governance frameworks must evolve in tandem with technological advancements. Current regulations in many countries lag behind the emergence of novel contaminants such as pharmaceuticals and microplastics. Future research should therefore support the development of regulatory standards that address these emerging threats and provide guidelines for the safe deployment of advanced technologies, particularly nanomaterials. Policymakers, industry stakeholders, and the scientific community must work collaboratively to ensure that technological innovations are accompanied by transparent governance, risk communication, and equitable implementation. Without such alignment, even the most advanced purification systems risk remaining confined to experimental settings rather than being scaled for global impact.
Taken together, future research in drinking water purification must move toward holistic, integrated solutions that bridge technical innovation with social, environmental, and economic considerations. Circular economy strategies, decentralized systems, renewable energy integration, digital intelligence, equity-focused design, multifunctional treatment approaches, climate resilience, and sustainability assessments will all play pivotal roles in shaping the next generation of water purification technologies. By embedding these priorities into the research agenda, the scientific community can contribute to resilient, inclusive, and sustainable solutions for one of humanity’s most pressing challenges.
Conclusion and Outlook
The purification of drinking water remains both a fundamental public health necessity and a growing environmental challenge. This review has highlighted the evolution of conventional treatment methods, including chlorination, flocculation, filtration, biological filtration, and adsorption, while also examining their respective strengths and limitations. These approaches continue to serve as the backbone of modern drinking water treatment systems; however, they are increasingly confronted with new and complex contaminants such as pharmaceuticals, pesticides, microplastics, and heavy metals. Moreover, global pressures including climate change, rapid urbanization, and the generation of toxic sludge further complicate the capacity of current technologies to safeguard public health and ensure water security.
The analysis also emphasizes that no single treatment method is universally effective across all contaminant categories. Chlorination, while highly effective for pathogen inactivation, risks the formation of harmful disinfection by-products. Flocculation and filtration provide reliable removal of suspended solids, yet their efficiency is constrained by issues such as fouling, sludge generation, and the persistence of dissolved organic and emerging contaminants. Biological filtration is sustainable and cost-effective but requires careful optimization of biofilm development and operational conditions. Adsorption, especially using materials such as activated carbon, zeolites, and silica, demonstrates considerable versatility but is limited by pollutant-specific selectivity and the inability to consistently meet stringent drinking water standards. These limitations underscore the need for integrated or hybrid systems that combine complementary mechanisms to achieve comprehensive purification.
Beyond conventional approaches, nanotechnology has emerged as a transformative frontier. Nanomaterials such as TiO2, Ag, ZnO, CuO, and Mn3O4 demonstrate exceptional antimicrobial and adsorptive properties, positioning them as highly promising candidates for advanced water purification. Nevertheless, significant barriers remain, including high production costs, potential ecotoxicity, and performance inconsistencies under real-water conditions. As discussed, future research must focus on overcoming these constraints through green synthesis methods, improved regeneration and reusability, and comprehensive safety assessments aligned with international regulatory frameworks. Integrating nanomaterials into hybrid treatment systems also holds promise for achieving multifunctionality, simultaneously addressing microbial pathogens, heavy metals, and organic contaminants.
Importantly, drinking water purification research must now be contextualized within broader global trends. Climate change not only threatens water availability through droughts and extreme weather events but also exacerbates risks of contamination and infrastructure failure. Population growth and urban expansion will further intensify water demand, requiring treatment solutions that are scalable, adaptable, and resilient. Emerging contaminants challenge the adequacy of current monitoring frameworks, highlighting the need for real-time sensing, predictive analytics, and smart water systems that integrate digital technologies with treatment processes.
Looking forward, the future of drinking water purification depends on a holistic approach that integrates technological innovation with sustainability, governance, and equity. Circular economy strategies that couple purification with resource recovery, decentralized point-of-use systems that extend safe water access to vulnerable populations, renewable energy-powered treatment technologies, and AI-driven optimization all represent critical frontiers for research and practice. Equally, social dimensions—such as affordability, community acceptance, and policy support—must be embedded into the design and deployment of future systems.
In conclusion, achieving universal access to clean and safe drinking water will require a paradigm shift from reliance on single, conventional methods toward the development of integrated, sustainable, and adaptive treatment solutions. By bridging material science, engineering innovation, environmental sustainability, and social responsibility, future water purification systems can rise to the dual challenge of protecting public health and ensuring water security in an era of unprecedented environmental change.
Data Accessibility Statement
The data supporting the findings of this review are entirely sourced from publicly available literature as cited in the present article. No original datasets were generated, and no unpublished data were used.
Acknowledgements
The authors thank Netherlands Maritime University College, Universiti Tun Hussein Onn Malaysia, Universiti Teknologi Malaysia, and Universiti Malaysia Pahang Al-Sultan Abdullah, Malaysia for supporting this work. All authors thank Assoc. Prof. Ts. Hairul Azmi Mohamed (Head of Coordinator, NMUC), Nur Ain Fatihah Abdul Razak (DiOSH Coordinator) and Aslina Ismail (BOSHM Coordinator), School of Occupational Safety and Health, NMUC, for the support and encouragement. In addition, the authors acknowledge the use of ChatGPT (OpenAI) for language editing and grammar improvement. All AI-assisted content was reviewed and verified by the authors to ensure accuracy, originality, and compliance with ethical standards.
Competing Interests
The authors have no competing interests to declare.