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Perchlorate in Drinking Water Frequent Questions


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Where is perchlorate found?

Perchlorate occurs naturally in arid states in the Southwest United States, in nitrate fertilizer deposits in Chile, and in potash ore in the United States and Canada. It also forms naturally in the atmosphere. Perchlorate can be manufactured and used as an industrial chemical and can be found in rocket propellant, explosives, fireworks and road flares. It has also been found in some public drinking water systems and in food.

Why is perchlorate in drinking water a health concern?

Perchlorate can disrupt the normal function of the thyroid gland in both children and adults. In adults, the thyroid plays an important role in metabolism, making and storing hormones that help regulate the heart rate, blood pressure, body temperature, and the rate at which food is converted into energy. In fetuses and infants, thyroid hormones are critical for normal growth and development of the central nervous system. Perchlorate can interfere with the human body's ability to absorb iodine into the thyroid gland which is a critical element in the production of thyroid hormones.

How does perchlorate get into my drinking water?

Perchlorate dissolves easily, is relatively stable and is mobile in water. While it has often been detected in water supplies in close proximity to sites where solid rocket fuel is manufactured or used, there are also locations in the United States lacking a clearly defined source.

Besides drinking water, how else can people be exposed to perchlorate?

People are exposed to perchlorate primarily through eating contaminated food or drinking water. The Food and Drug Administration (FDA) Total Diet Study combines nationwide sampling and analysis of hundreds of food items along with national surveys of food intake to develop comprehensive dietary exposure estimates for a variety of demographic groups in the U.S. The complete set of FDA perchlorate data can be found here:

How do I know if perchlorate is in my water?

Contact your local water supplier to find out if perchlorate is in  your drinking water and what steps your utility is taking to reduce your exposure. If you don't know who your local water supplier is, the information should be included in your latest water bill. 

Can perchlorate be boiled out of my water?

No, perchlorate cannot be removed by heating or boiling water.

How does a utility reduce/remove perchlorate?

A number of options are available to drinking water systems to lower concentrations of perchlorate in the drinking water supply. In some cases, drinking water systems may be able to reduce concentrations of perchlorate by closing contaminated wells or changing rates of blending of water sources.
Perchlorate can be removed using a number of advanced treatment technologies. Each technology has advantages and disadvantages depending on the level of perchlorate present in the source water, removal goals, other water quality parameters, competing treatment objectives, and treatment waste disposal options. Regenerable and single-pass ion exchange, reverse osmosis, and fixed- and fluidized-bed biological treatment can all remove perchlorate from drinking water sources.
These treatment technologies are used by some public water systems today and should be carefully designed and maintained to ensure that they are effective for treating perchlorate. 

I get my tap water from a private well. How can I find out if perchlorate is in my water?

If you are concerned about the possibility of perchlorate in your drinking water and you are served by a private well, EPA recommends testing your drinking water. Approved laboratories can analyze a sample of your water to determine whether perchlorate is present and at what concentrations. More information about private wells can be found here:

Why did EPA decide to regulate perchlorate?

The Safe Drinking Water Act (SDWA) requires that once every five years, EPA issue a Contaminant Candidate List (CCL). The CCL is a list of contaminants that are currently not subject to any proposed or promulgated national primary drinking water regulations, but are known or anticipated to occur in public water systems. Perchlorate was a part of CCL1 (1998), CCL2 (2005) and CCL3 (2009). In addition, EPA issues an Unregulated Contaminant Monitoring Rule (UCMR) to identify up to 30 unregulated contaminants to be monitored by large public water systems (PWSs) and a subset of small PWSs across the U.S. The UCMR provides EPA and other interested parties with nationally representative data on the occurrence of particular contaminants in drinking water.  This data set lets the Agency assess the number of people potentially being exposed and provides an estimate of the levels of that exposure. Perchlorate was included in UCMR 1 (2001- 2005).  
After issuing a CCL, EPA must decide whether to regulate at least five or more contaminants on the list (called Regulatory Determination). A Regulatory Determination is a formal decision on whether (or not) EPA should initiate a rulemaking process to develop a regulation for a specific contaminant or group of contaminants. In 2011, EPA announced its decision to regulate perchlorate under the Safe Drinking Water Act (SDWA). Specifically, EPA determined that perchlorate meets SDWA's criteria for regulating a contaminant--that is, perchlorate may have an adverse effect on the health of persons; perchlorate is known to occur or there is a substantial likelihood that perchlorate will occur in public water systems with a frequency and at levels of public health concern; and in the sole judgment of the Administrator, regulation of perchlorate in drinking water systems presents a meaningful opportunity for health risk reduction for person served by public water systems.

Has a safe level of exposure for perchlorate been established?

EPA has not yet established a maximum contaminant level goal for perchlorate. The MCLG is the maximum level of a contaminant in drinking water at which no known or anticipated adverse effect on the health of persons would occur, allowing an adequate margin of safety. On February 11, 2011, EPA determined that perchlorate meets the Safe Drinking Water Act criteria for regulation as a contaminant. The Agency found that perchlorate may have an adverse effect on the health of persons and is known to occur in public drinking water systems with a frequency and at levels that present a public health concern. Since that time, EPA has been reviewing the best available scientific data on a range of issues related to perchlorate in drinking water including its occurrence, treatment technologies, analytical methods and the costs and benefits of potential standards.
There also have been state actions on perchlorate such as standards, guidelines and advisories. In 2006, Massachusetts adopted a drinking water standard for perchlorate of 2 µg/L, and in 2007, California promulgated a standard of 6 µg/L. Twelve other states have established non-enforceable guidance, action or advisory levels. Depending on the state, a particular level may require a public water system to notify the public, serve as a screening tool for further action, or guide clean-up actions.
Customers that are served by a public water system can contact their local water supplier and ask for information on perchlorate in their drinking water.