Optical sensing technologies coupled with IoT for water quality assessment: a review

Clean water remains a vital resource for life, however, urbanization and industrialization continue to degrade its quality, emphasizing the urgent need for advanced monitoring. Despite advances in water monitoring sensors, there remains a critical research gap: the lack of cost-effective, scalable Internet of things (IoT)-integrated optical sensing frameworks for real-time detection in remote or resource-limited settings, where traditional methods often fail due to high costs (>$500/unit) and limited portability. This study addresses this by reviewing recent (2018–2025) IoT-enabled optical sensor designs for Water Quality Monitoring , analyzing over 100 studies on integration strategies for optical, networking, and electronic components, and conducting a comparative evaluation of performance metrics like stability, detection limits (e.g., ppb-level for heavy metals), and connectivity. Different materials perform various optical phenomena such as colourimetry, photoluminescence, Förster resonance energy transfer, and Surface Plasmon Resonance that are used for sensing the contaminants. Key findings reveal that hybrid carbon quantum dots-based optical sensors with IoT achieve better sensitivity and cost effectiveness compared to conventional devices, but face challenges in long-term stability and edge computing latency. We propose a novel modular framework for future IoT-optical systems, emphasizing receptor material, device design and development, and AI-driven data fusion to enhance reliability.