History and assessment of household Arsenic Biosand Filter interventions in Nepal: Over two decades of efforts and challenges

Arsenic contamination found in groundwater poses a significant number of health risks, particularly within rural regions of developing countries. In Nepal, the introduction of the Arsenic Biosand Filter (ABF) as a household-level intervention aimed to mitigate arsenic exposure in the arsenic-affected Terai region. Despite its initial promise, questions remain regarding the filter's long-term performance, user awareness, and the sustainability of its dissemination. This study examines the historical development, implementation, and current status of ABFs in the Nawalparasi West District—a commonly known arsenic hotspot—over more than two decades. It is conducted through an integrated review of past documentation; oral histories of involved personnel; and household surveys, which includes an evaluation of filter performance. Among 1044 active ABFs tested, 17 % of raw water samples from tube wells exceeded 50 μg/L, while 4.3 % of filtered water samples still failed to meet Nepal's standard. Filter effectiveness decreased linearly as arsenic concentrations increased. While arsenic contamination in groundwater was generally limited, highly contaminated areas were concentrated in specific locations, necessitating targeted interventions that can effectively address localized risks. Findings reveal low arsenic awareness among users (80 % of which being unaware) and significant disparities in the provided filters, which were linked to both user maintenance practices and supply chain quality. Nevertheless, the study underscores the contributions of local initiatives and scale-up efforts in advancing sustainable arsenic mitigation through coordinated actions and entrepreneurship in the dissemination of ABFs. The results advocate for improved awareness programs targeted at groups with lower educational attainment, enhanced product monitoring by coordinating agencies, and affordable water quality testing mechanisms to ensure long-term sustainability. • Among 1044 tested samples from tube wells, 17 % exceeded 50 μg/L of arsenic. • High concentrations are in specific areas, necessitating localized interventions. • Filter effectiveness decreased linearly as arsenic concentration increased. • Low user awareness and disparities in filter product quality are critical gaps. • Enhanced product monitoring and affordable water testing mechanisms are recommended.