Summary
A component of rocket fuel, flares and fireworks, perchlorate occurs both naturally and as a synthetic chemical.
Perchlorate blocks the thyroid from taking in iodide, which is critical to the thyroid’s ability to regulate many body functions. Too little iodide can lead to an array of health problems, including reduced thyroid hormones, and it can negatively impact metabolism, and physical and cognitive development.
Children and the developing fetus are most at risk from perchlorate exposure, because their brains are still developing and their bodies are highly sensitive to smaller fluctuations in iodide levels. Changes in thyroid hormone levels during pregnancy can cause lasting harm, since the thyroid system governs fetal brain development.
There’s no enforceable federal limit on perchlorate in drinking water. Some states have stepped up in the absence of a U.S.-wide policy. Massachusetts has the most health-protective regulation for the chemical in the country, allowing no more than 2 parts per billion, or ppb in drinking water. Arizona, California, New Jersey, New York and Texas also regulate perchlorate in drinking water. California set a public health goal of 1 ppb in 2015, although its legal limit remains 6 ppb. EWG recommends a limit of no more than 1 ppb perchlorate in drinking water to protect children from its harms.
In 2011, the Environmental Protection Agency determined that perchlorate met the Safe Drinking Water Act criteria for regulation, based on its potential health effects. However, in 2020 the Trump EPA reversed the decision and announced it would not set a drinking water standard, a move that was challenged in court. In 2023, a federal appeals court ruled against the EPA's reversal and found the agency must regulate perchlorate in drinking water. In 2024, the Biden EPA agreed to such a standard by 2026.
Click here to see nationwide test results for perchlorate.
Where is perchlorate found, and why is it in food and drinking water?
Perchlorate is very mobile in soil and groundwater, and does not readily degrade – this can lead to underground pollution of drinking water supplies. High levels of contamination may be found near manufacturing facilities, defense contracting sites and military operations. The defense and aerospace industries use 90 percent of domestically produced perchlorate.
EPA-mandated tests between 2001 and 2003 found perchlorate in U.S. drinking water systems serving more than 16.6 million people. These tests underestimated the extent of perchlorate pollution, because they did not include smaller water systems and private water wells. The EPA has not required any further testing.
New studies show that perchlorate has also now contaminated irrigation water, fertilizer and food. Perchlorate is detectable in nearly all produce, dairy products and packaged foods, accounting for an estimated 80 percent of Americans' exposure.
What can I do if there is perchlorate in my water?
If EWG’s Tap Water Database shows perchlorate has been detected in your water supply, or if a test of your private well has found the chemical, select a home water filter that uses reverse osmosis to reduce the level of contamination. Make sure any system you purchase is certified to remove perchlorate. You can find EWG’s Water Filter Guide here.
If you have perchlorate in your drinking water and are pregnant or breastfeeding, or have young children at home, it is best to drink only filtered water during this critical period of sensitivity.
References
California Office of Environmental Health Hazard Assessment, Updated Public Health Goal for Drinking Water: Perchlorate. 2015. Available at https://oehha.ca.gov/media/downloads/water/chemicals/perchloratephgfactsheet.pdf
Environmental Defense Fund, FDA Finds More Perchlorate in More Food, Especially Bologna, Salami and Rice Cereal. 2017. Available at blogs.edf.org/health/2017/01/09/fda-finds-more-perchlorate-in-more-food/
Environmental Defense Fund, EPA to Consider Perchlorate Risks from Degradation of Hypochlorite Bleach. 2017. Available at blogs.edf.org/health/2017/02/03/perchlorate-risks-from-bleach/
Philip Brandhuber et al. A Review of Perchlorate Occurrence in Public Drinking Water Systems. Journal AWWA, 2009, 101;11. Available at www.epa.gov/sites/production/files/2015-09/documents/12004-exhibita.pdf
Environmental Protection Agency, Fact Sheet: Final Regulatory Determination for Perchlorate. 2011. Available at www.epa.gov/sites/production/files/2015-08/documents/epa815f11003.pdf
EPA, Technical Fact Sheet – Perchlorate. 2014. Available at https://19january2017snapshot.epa.gov/sites/production/files/2014-03/documents/ffrrofactsheet_contaminant_perchlorate_january2014_final.pdf
EPA, Consent Decree. 2016. Available at blogs.edf.org/health/files/2016/12/Perchlorate-NRDC-v-EPA-2-16-cv-01251-ER-Consent-Decree-Entered-10-19-16.pdf
Food and Drug Administration, Preliminary Estimation of Perchlorate Dietary Exposure Based on FDA 2004/2005 Exploratory Data. 2007. Available at www.fda.gov/Food/FoodborneIllnessContaminants/ChemicalContaminants/ucm077653.htm
FDA, Perchlorate Questions and Answers. 2015. Available at www.fda.gov/Food/FoodborneIllnessContaminants/ChemicalContaminants/ucm077572.htm#epahealth
Massachusetts Department of Environmental Protection, 310 CMR 22.06 Inorganic Maximum Contaminant Levels (MCLs). 2016. Available at https://www.mass.gov/doc/drinking-water-standard-for-perchlorate/download
February 2025