Questionnaire
At baseline and follow-up visits, each participant was administered an in-person structured questionnaire on demographics, behavioral determinants, water use, and other study factors. Questionnaire interviews were conducted by trained research assistants from MBIRI. Due to the COVID pandemic, some visits were delayed, with an average duration between baseline and final follow-up of 2 years. The primary participant in each household was additionally administered a household-level questionnaire assessing the condition of the POU arsenic filter, technical issues related to use, and if the arsenic filter cartridge was changed since the previous visit.