EWG's Tap Water Database



July 2017


Perchlorate, a component of rocket fuel, flares and fireworks, occurs both naturally and as a synthetic chemical. EWG’s Tap Water Database includes records of perchlorate detected in 215 water utilities serving an estimated 9 million people. Widespread contamination of water has resulted in perchlorate contamination of most of our food and milk supplies. In the body, perchlorate interferes with iodine uptake in the thyroid which can result in reduced thyroid hormones and an impact on metabolism, and physical and cognitive development. Children and developing fetuses are the most at risk from perchlorate contamination.

Perchlorate is the only unregulated contaminant for which the EPA has attempted to set a federal drinking water standard since 1996. However, the agency has yet to propose a draft limit, let alone a final one. The Department of Defense and military contractors who have used and released large quantities of perchlorate have actively lobbied against regulation. 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, but its legal limit remains 6 ppb.

Click here to see the nationwide testing 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, enabling 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 testing between 2001 and 2003 found perchlorate in drinking water systems serving over 16.6 million people. This testing underestimated the extent of perchlorate pollution because it didn’t include smaller water systems and people drinking well water, and the reporting limit was 4 ppb, though California has deemed water concentrations greater than 1 ppb to pose a health concern. This testing spurred EPA to initiate rule making for perchlorate in drinking water, and some water utilities to install filters to reduce perchlorate contamination.

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 which helps regulate many body functions, including metabolism, growth of the brain and neurological development. Infants and fetuses are more susceptible to the effects of perchlorate than adults because their brains are quickly developing and their bodies are more sensitive to smaller changes in iodide levels. Changes in thyroid hormone levels during pregnancy can have a lasting impact, as the thyroid system governs fetal brain development.

Why is perchlorate only regulated in a few states?

The EPA does not currently regulate perchlorate in drinking water, despite announcing its intent to do so in February 2011. Based on the 1996 amendments to the Safe Drinking Water Act, the EPA is required to publish a proposed regulation within two years and finalize the regulation within a year and half. Yet, to date, pressure from the aerospace industry and the Department of Defense have hindered the EPA’s ability to proposed a regulation for perchlorate. Under a consent decree, the EPA agreed to publish a proposed regulation by October 2018.

Several states have moved faster than the EPA to set legal standards and goals for perchlorate in water. The most protective regulation is in Massachusetts which set a legal limit of 2 ppb in 2006. In 2015, California published a public health goal value of 1 ppb for perchlorate in drinking water, which accompanies a legal maximum contaminant level of 6 ppb which was set in 2007.

How can we get perchlorate out of water?

Based on the current best available science, EWG would support a national legal limit that matches the California public health goal of 1 ppb. But the EPA should also investigate people’s exposure to perchlorate from food. The acceptable level of perchlorate in drinking water could decrease to account for increasing contamination of dairy products and produce.

In May 2017 the Food and Drug Administration declined to revoke its approval of perchlorate as a food packaging additive, countering a petition from EWG, Breast Cancer Fund, Center for Environmental Health, Center for Food Safety, Center for Science in the Public Interest, and Natural Resources Defense Council. The FDA must investigate and reduce controllable sources of perchlorate in the food supply, and it should strictly regulate the use of bleach to minimize the potential for perchlorate formation, especially in instances that may increase human ingestion of perchlorate.

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

If perchlorate is detected in your water you can use a home water filter employing reverse osmosis to reduce the level. 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, breastfeeding or have a young child at home, it is wise during this critical period of sensitivity to drink only filtered water.


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

EPA, Fact Sheet: Final Regulatory Determination for Perchlorate. 2011. Available at

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

EPA, Consent Decree. 2016. Available at

FDA, 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