Unravelling fouling characteristics in a point-of-use water purifier: Bridging compositional evolution to spatial distribution

• Distinct inorganic–organic-biological combined fouling patterns were observed across five stages. • Pre-AC exhibited the highest organic foulants adsorption and promoted biofilm formation. • IER demonstrated greatest Ca 2+ and Mg 2+ removal efficiency, highlighting its softening function. • Contaminants rejection by the RO membrane led to the foulants accumulation on its surface. • Prolonged operation of post-AC result in Al/Fe/Si accumulation and Mycobacterium colonization. With the rapid advancement of water purification technologies, point-of-use (POU) water purifiers have become essential for delivering clean water. However, the foulants accumulation during operation can lead to a deterioration in water quality and a shortening of operational lifespan. A comprehensive analysis of fouling characteristics, considering compositional evolution to spatial distribution, is crucial for ensuring stable operation and optimizing performance. This study analyzed the fouling characteristics in a POU water purifiers across five stages: polypropylene (PP) cotton, pre-activated carbon (AC), ion exchange resin (IER), reverse osmosis (RO) membrane, and post-AC, revealing stage-specific inorganic–organic-biological fouling patterns driven by material interactions and dynamic water quality changes. PP cotton stage primarily captures Al/Fe/Si-contained colloidal foulants, while pre-AC shows the highest organic adsorption capacity, subsequently promoting diverse biofilm growth, underscoring the necessity of implementing catalytic AC to enhance removal and degradation efficiency. IER accumulates the highest Ca and Mg content, whereas the size exclusion mechanism of RO membrane results in relatively low foulant accumulation. Long-term operation leads to accumulation of inorganic–organic-biological combined foulants in post-AC, including potential pathogens Mycobacterium , emphasizing the need for advanced mitigation strategies such as ultraviolet sterilization or the use of silver-impregnated AC to ensure water safety. The findings provide fundamental insights into stage-specific fouling mechanisms that have guided the development of optimization strategies encompassing functional material application, treatment process design, and system operation management.