Safe drinking water is essential, yet millions of people remain exposed to contaminated supplies. Conventional treatments such as chlorination and UV light can kill microbes, but they also create harmful byproducts, face resistance issues, and are not always sustainable. Green-synthesized nanomaterials (GSNMs) are emerging as an eco-friendly alternative. Produced with plants, microbes, algae, and natural polymers, these materials merge nanotechnology with green chemistry. Among them, silver, zinc oxide, copper oxide, titanium dioxide, and graphene-based nanomaterials show strong antimicrobial effects by disrupting membranes, generating reactive oxygen species (ROS), and damaging genetic material. Compared with chemically made nanoparticles, GSNMs are often safer, cheaper, and more environmentally compatible. Nevertheless, concerns about toxicity, environmental fate, and large-scale use remain. This review highlights recent progress in GSNM synthesis, antimicrobial mechanisms, and safety considerations, highlighting their potential to enable sustainable water disinfection while identifying critical areas for further research.

Arsenic contamination in water poses a significant global health risk, necessitating efficient and sustainable remediation strategies. Arsenic contamination affects groundwater in at least 106 countries, potentially exposing over 200 million people to elevated levels, primarily through contaminated drinking water. Among the most affected regions, Bangladesh remains a critical case study, where widespread reliance on shallow tubewells has resulted in one of the largest mass poisonings in history. Bio-based nanomaterials have emerged as promising solutions due to their eco-friendly nature, cost-effectiveness, and high adsorption capabilities. These nanomaterials offer a sustainable approach to arsenic remediation, utilizing materials like biochar, modified biopolymers, and bio-based aerogels, which can effectively adsorb arsenic and other pollutants. The use of environmentally friendly nanostructures provides a potential option for improving the efficiency and sustainability of arsenic remediation from groundwater. This review explores the mechanisms underlying arsenic remediation using such nanomaterials, including adsorption, filtration/membrane technology, photocatalysis, redox reactions, complexation, ion exchange, and coagulation–flocculation. Despite their potential, challenges such as scalability, stability, and regeneration hinder widespread application. We discuss recent advancements in material design, surface modifications, and hybrid systems that enhance performance. Finally, future perspectives are highlighted, including the integration of these bio-derived systems with smart sensing technologies, sustainable water-treatment frameworks, smart design, and life-cycle integration strategies, particularly for use in resource-constrained regions like Bangladesh and other globally impacted areas.