The Environmental Protection Agency (“EPA”) is responsible for setting federal limits on chemicals allowed in public drinking water. The limit for a contaminant typically reflects a level believed to protect human health, but that public water systems can achieve using the best available technology. To date, EPA has adopted regulations setting national limits on over 90 contaminants in drinking water. However, since the 1990s, only one chemical has come close to regulation: perchlorate.

Perchlorate is a chemical widely used by the military and defense industries in solid rocket propellants, fireworks, and other explosives, matches, and signal flares. According to EPA, at certain levels, perchlorate can prevent the thyroid gland from receiving enough iodine, which can affect thyroid hormone production. For pregnant women with low iodine levels, sufficient changes in thyroid hormone levels may cause changes in the child’s brain development. For infants, changes to thyroid hormone function can also impact brain development.

A potential national drinking water standard for perchlorate has been hotly debated for years. In 2008, the federal government formally declined to set a drinking water standard for this constituent. In 2011, EPA found that a drinking water standard for perchlorate was necessary to protect human health, which then triggered a legal duty to regulate the chemical under the Safe Drinking Water Act (“SDWA”). In 2016, the Natural Resources Defense Council sued EPA for failing to fulfill this duty and this ultimately resulted in a court-approved consent decree requiring EPA to propose a national perchlorate drinking water standard by 2018. The proposed standard should have been finalized by late 2019, but after several extensions, it is currently due in June 2020.

EPA has not formally announced a final decision regarding its plans to regulate perchlorate. However, news outlets have recently begun reporting that EPA plans to back away from establishing a federal limit on perchlorate in drinking water. Irrespective of the federal decision regarding perchlorate, this constituent does not exist wholly unregulated. The SDWA allows states to set and enforce their own drinking water standards, so long as the standards are, at a minimum, as stringent as EPA’s national standards. Today, California remains one of only a few states that regulate perchlorate in drinking water. The maximum contaminant limit for perchlorate in California is 6 micrograms per liter.

As a public water purveyor or other regulated entity, remaining compliant and following evolving agency decisions can be challenging. If you need assistance, we are here to help. Please contact us at

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PDF-The Long-Standing Fight for Setting Federal Limits on Perchlorate in Drinking Water May Be Nearing an End

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