According to a study recently published in Environmental Health, exposure to arsenic in drinking water, even at low levels, can cause cognitive impairment. Researchers from Columbia University and the University of New Hampshire followed 272 school children from three school districts in Maine for five years. After adjusting for social factors, the researchers concluded that on average, exposure to arsenic in well water was associated with decreased IQ scores and perceptual reasoning, working memory, and verbal comprehension scores. Exposures as low as 5 parts per billion (ppb) correlated with IQ scores 5-6 points lower than average. EPA’s standard for arsenic in public drinking water is 10 ppb, but there is no limit for private wells, which provide drinking water to more than 13 million Americans. Based on data indicating that between 10-20% of private wells have arsenic concentrations greater than 5 ppb, thousands of Americans may be at risk for cognitive impairment.