The EPA issued a final determination to regulate perchlorate on February 11, 2011. The EPA's 2011 determination was based upon the three criteria for regulation under the Safe Drinking Water Act: 1) The EPA determined that perchlorate may have adverse effects on the health of persons based upon the National Research Council's study that found perchlorate inhibits the thyroid's ability to uptake iodide needed to produce hormones. 2) The EPA concluded that perchlorate occurs with frequency at levels of health concern in public water systems based upon data collected under the first Unregulated Contaminant Monitoring Rule (UCMR 1) from 2001 to 2005. Monitoring results reported to the EPA under UCMR 1 show that perchlorate was measured in over four percent of water systems. 3) The EPA concluded that there was a meaningful opportunity to protect public health through a drinking water regulation by reducing perchlorate exposure for the 5 to 17 million people who may be served perchlorate in their drinking water. In 2013, the Science Advisory Board (SAB) recommended that the EPA use models, rather than the traditional approach to establish the health-based maximum contaminant level goal for a perchlorate regulation. The EPA and FDA scientists worked collaboratively to develop biological models in accordance with SAB recommendations. The EPA completed peer review of this analysis in March 2018. The EPA will utilize the best available, peer-reviewed science to inform regulatory decisionmaking for perchlorate.