Perchlorate is a chemical that forms naturally in the atmosphere and occurs naturally in arid states in the Southwest United States. It can also be found in some fertilizers. In manufacturing, perchlorate and its salts are used in solid propellant for rockets, missiles and fireworks, and for the production of matches, flares, pyrotechnics, ordnance and explosives. Their use can lead to releases of perchlorate into the environment.

Perchlorate is a regulated drinking water contaminant in California, with a maximum contaminant level (MCL) of 6 parts per billion (ppb or µg/L). The MCL became effective October 2007. The State of California Division of Drinking Water (DDW) lowed detection limit for purposes of reporting (DLR) for perchlorate to 2 ug/L in 2021 and then to 1 ug/L in January of 2024. This was done to gather new perchlorate occurrence data at lower levels. After reviewing the occurrence data, the DDW may recommend a revised (lower) MCL.

Golden State Water routinely monitors and tests for more than 230 contaminants, including perchlorate, to ensure the water we deliver to customers meets all state and federal drinking water standards. Golden State Water makes water quality information available via annual Consumer Confidence Reports (CCR).

Water quality test results are directly submitted by the State certified laboratory to the State of California’s Division of Drinking Water (DDW) and recorded on the State’s website for full transparency. Click here to view test results on the DDW website.

As your water provider, we continually invest in water infrastructure, treatment and testing and take great pride in providing you with high-quality, reliable water.

Frequently Asked Questions

Q:  Has perchlorate been found in my drinking water?
A:  In 2017, perchlorate at levels below the current MCL was detected in treated drinking water in two of our 37 water systems. Some of Golden State Water’s groundwater sources contain perchlorate levels above the MCL. Water from these wells is treated using ion exchange to remove perchlorate to levels below the MCL.

The water served to customers in each of Golden State Water’s water systems meets all state and federal drinking water standards for safety, including the perchlorate MCL. Click here to see the most recent results for perchlorate levels detected in our treated drinking water.

Q:   How is perchlorate removed from contaminated source waters?
A:  Perchlorate can be removed using a number of advanced drinking water treatment technologies, including ion exchange, reverse osmosis, and fixed- and fluidized-bed biological treatment. Golden State Water uses ion exchange to treat its drinking water sources with perchlorate levels above the MCL.

Resources for Additional Information

State Water Resources Control Board
U.S. Environmental Protection Agency
U.S. Environmental Protection Agency (Perchlorate FAQ)