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• Arsenic-contaminated water is a major public health issue in India and Bangladesh. • Laterite soil provides a novel and cost-efficient way of removing arsenic from water. • A mathematical model determines filter lifetime and an upscaling protocol. • The model captures the filter behaviour through three simple parameters. • The model plays an essential role in the filter deployment and maintenance. Arsenic is among the most hazardous contaminants present in drinking water. Recent increase in agricultural growth and fertiliser use in India and Bangladesh has led to the release of naturally occurring arsenic from the rocks, creating a major public health issue. A novel technology has been developed using naturally abundant laterite soil to filter arsenic, providing potable water to more than 5000 people. To upscale this technology and realise its full potential, a comprehensive understanding of the dependence of filter life on operating regime (flow rate, arsenic concentration and filter size) is essential. We present a mathematical model that characterises arsenic removal, circumventing the need for time-consuming experiments. The model incorporates inter- and intra-particle mass transport within the filter medium. The resulting model enables prediction of a filter lifetime in a specified role, such as on a domestic or community scale, and should assist in future filter deployment and maintenance. [ABSTRACT FROM AUTHOR]