In our study, nearly a third of homes with children reported exclusively drinking bottled/filtered water at home. It is likely these practices are even more prevalent in areas with greater levels of contaminants. Failure to take even modest use of filters or bottled water into account during sample size calculations and analysis might substantially impair the ability to detect associations in studies in which the contaminant of interest is removed by the most common types of filters, and for which the main route of exposure is ingestion as opposed to absorption/inhalation during bathing, showering and swimming. For arsenic and nitrate, this might be less problematic if reverse osmosis devices are uncommon, as we observed. Nonetheless, their use should be taken into consideration if possible [10].