EWG's Tap Water Database — 2019 UPDATE

picture of test tube and beaker in laboratory


October 2019


A component of rocket fuel, flares and fireworks, perchlorate occurs both naturally and as a synthetic chemical. EWG’s Tap Water Database includes records of perchlorate detected in 375 water utilities serving an estimated 12.1 million people. 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 detrimental health effects, including reduced thyroid hormones and an impact on metabolism, and physical and cognitive development. Children and developing fetuses are most at risk from perchlorate contamination.

Massachusetts has the most health-protective drinking water regulation for the chemical in the country, at 2 parts per billion, or ppb. The presence of perchlorate in drinking water is also regulated in Arizona, California, New Jersey, New York and Texas. California set a public health goal of 1 ppb in 2015, although its legal limit remains 6 ppb. EWG recommends a Maximum Contaminant Level of no more than 2 ppb perchlorate in drinking water, and ideally 1 ppb, to protect children from the health harms caused by perchlorate.

Click here to see the 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. These characteristics lead to the formation of underground pollution. High levels of contamination may be found around manufacturing facilitates, 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 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 those who drink well water.

New studies have highlighted the fact that perchlorate has also now contaminated irrigation water, fertilizer and food. Perchlorate is detectable in nearly all produce, dairy products and packaged foods – the sources of an estimated 80 percent of Americans' exposure.

Why is perchlorate harmful?

Perchlorate blocks the ability of the thyroid to take in iodide, which can lead to an array of detrimental health effects. Iodide is critical in the thyroid, because it is a component of the thyroid hormone that helps regulate many body functions, including metabolism, growth of the brain and neurological development. Infants and fetuses are especially susceptible to the effects of perchlorate, 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 have a lasting impact, since the thyroid system governs fetal brain development.

What can I do if there is perchlorate in my water?

If perchlorate is detected in your water, select a home water filter that uses reverse osmosis to reduce the level of contamination. You can find EWG’s water filter guide here. Make sure any system you purchase is certified to remove perchlorate. If you have perchlorate in your drinking water and are pregnant or breastfeeding, or have young children at home, it is best during this critical period of sensitivity to drink filtered water only.


California Office of Environmental Health Hazard Assessment, Updated Public Health Goal for Drinking Water: Perchlorate. 2015. Available at

Environmental Defense Fund. FDA Finds More Perchlorate in More Food, Especially Bologna, Salami and Rice Cereal. 2017. Available at

Environmental Defense Fund, EPA to Consider Perchlorate Risks from Degradation of Hypochlorite Bleach. 2017. Available at

Philip Brandhuber et al. A Review of Perchlorate Occurrence in Public Drinking Water Systems. Journal AWWA, 2009, 101;11. Available at

Environmental Protection Agency. Fact Sheet: Final Regulatory Determination for Perchlorate. 2011. Available at

EPA, Technical Fact Sheet – Perchlorate. 2014. Available at

EPA, Consent Decree. 2016. Available at

Food and Drug Administration. Preliminary Estimation of Perchlorate Dietary Exposure Based on FDA 2004/2005 Exploratory Data. 2007. Available at

FDA, Perchlorate Questions and Answers. 2015. Available at

Massachusetts Department of Environmental Protection, 310 CMR 22.06 Inorganic Maximum Contaminant Levels (MCLs). 2016. Available at