Naturally occurring arsenic in groundwater in Cambodia is a serious health concern. This study tested the efficacy of a BioSand filter amended with iron nails, Kanchan filter, as a household water treatment option with three natural arsenic-bearing groundwater sources of varying compositions and spiked with lab cultured E. coli and MS2. The effectiveness of arsenic and pathogen removal was not constant over time and was highly dependent on the influent composition. The filter was relatively ineffective in treating arsenic contaminated groundwater and effluent arsenic concentrations were between 74 and 2206 microg L(-1), which is higher than accepted drinkng water standards. The overall average arsenic removal was 39.4, 74.9, and 45.4%, respectively, and the extent of arsenic removal was not related to the influent arsenic concentration. The main reasons for poor arsenic removal was due to the combination of high influent P (> 0.5 mg L(-1)) and low Fe (< 5 mg L(-1)) concentrations and that the added iron nails were largely ineffective due to insufficient contact time withthe water. The findings suggest that such amended filters should not be widely deployed until improvements are made to address the consistency and efficacy of treatment In addition, the filter poses some potential health risk associated with the production of elevated nitrate levels in the effluent within the filter, possibly due to nitrification and high levels of ammonia in the groundwater.