Perchlorate

Perchlorate is a inorganic chemical regulated in US drinking water. Rocket propellant, explosives, and fireworks manufacturing; some natural fertilizer deposits.

No final federal MCL in effect. EPA made a regulatory determination in 2011 but withdrew it in July 2020, concluding a national limit would not meaningfully reduce health risk. In May 2023 the U.S. Court of Appeals for the D.C. Circuit (NRDC v. Regan) vacated that 2020 withdrawal, holding EPA lacked authority under the Safe Drinking Water Act to rescind its 2011 decision to regulate. Under a resulting consent decree, EPA proposed a national perchlorate rule in January 2026 — a proposed MCLG of 0.02 mg/L (20 ug/L) with co-proposed MCL options of 20, 40, or 80 ug/L, open for public comment through March 9, 2026, and a final rule due by May 21, 2027. As of this dataset's vintage that rule is proposed, not final, so no enforceable federal limit yet exists. Some states already regulate it (California 6 ppb; Massachusetts 2 ug/L).

Interferes with the thyroid's ability to take up iodine, which can disrupt production of thyroid hormone — a particular concern for fetuses, infants, and people with hypothyroidism.

EPA's enforcement data (SDWIS/ECHO) records zero violations of Perchlorate's rule nationally. See this contaminant's regulatory status above for its current standard and compliance timeline — a zero count is not necessarily an all-clear.

Filter technologies certified to reduce Perchlorate include: reverse osmosis (NSF/ANSI 58), anion exchange (NSF/ANSI 53). Look for a filter independently certified against the specific NSF/ANSI standard for this contaminant — general "reduces contaminants" marketing claims are not the same as a contaminant-specific certification.