Perchlorate is a chemical you've likely never heard of, yet it may be in your tap water right now. This odorless, tasteless contaminant is a key component of rocket fuel and explosives, and it has contaminated the drinking water supplies of approximately 40 communities across the United States, with the heaviest concentrations in California, Nevada, and Texas. Unlike lead or bacteria, perchlorate doesn't make water look cloudy or smell bad. But its health effects, particularly for infants and pregnant women, are serious enough that the EPA has been evaluating it for regulation for nearly two decades. The challenge: perchlorate is not yet federally regulated, which means your water utility may not be testing for it or telling you about it. This guide explains what perchlorate is, where it comes from, what health risks it poses, and most importantly, what you can do to protect yourself and your family.
What Is Perchlorate and Why Is It in Drinking Water?
Perchlorate (chemical formula ClO4-) is an inorganic chemical compound that has been manufactured and used in the United States since the 1950s. Its primary uses include rocket propellant, explosives, fireworks, and certain types of fertilizers. Because perchlorate dissolves easily in water and breaks down very slowly in the environment, it can persist in groundwater for decades or even longer.
Perchlorate enters drinking water supplies through two main pathways. First, direct contamination occurs near military bases, aerospace manufacturing facilities, and weapons testing sites where perchlorate has been stored, handled, or disposed of improperly. Second, indirect contamination happens when perchlorate from fertilizers used in agriculture leaches into groundwater and eventually reaches drinking water aquifers. Some water supplies have been contaminated by both sources.
The geographic distribution of perchlorate contamination is heavily concentrated in the Southwest and California. Nevada has the most significant contamination, with the Las Vegas valley being one of the most affected regions in the nation. Southern California's Colorado River Basin and areas around Los Angeles also show high levels. Texas, particularly in the western regions near El Paso and military installations, has detected perchlorate in multiple water systems. Other states including Florida, Massachusetts, New Mexico, and Oklahoma have also found perchlorate in their supplies, though often at lower concentrations.
Health Effects of Perchlorate Exposure
How Perchlorate Affects the Thyroid
The primary health concern with perchlorate relates to thyroid function. Perchlorate interferes with iodide uptake in the thyroid gland, a process essential for producing thyroid hormones. These hormones regulate metabolism, growth, and development. When perchlorate blocks iodide uptake, the thyroid must work harder to produce adequate hormones, potentially leading to hypothyroidism (an underactive thyroid) or thyroid enlargement.
For most healthy adults with adequate iodine intake, low-level perchlorate exposure through drinking water is unlikely to cause noticeable thyroid problems. The body can often compensate for minor reductions in iodide availability. However, certain populations are at higher risk: individuals with existing iodine deficiency, people with pre-existing thyroid disease, and those taking medications that affect thyroid function are more vulnerable to perchlorate's effects.
Risk to Infants and Developing Fetuses
The most concerning health effects from perchlorate occur during pregnancy and infancy. The EPA and multiple scientific studies have identified infants and unborn children as the populations most susceptible to harm from perchlorate exposure. A major 2006 study published by researchers at the Centers for Disease Control and Prevention found that perchlorate was detected in urine samples from over 97 percent of Americans tested, indicating widespread exposure in the general population.
During pregnancy, the developing fetus relies on maternal thyroid hormones for normal growth and neurological development, particularly in the first trimester. Adequate thyroid hormone is critical for brain development, and even modest reductions in maternal thyroid hormone levels have been associated with slightly lower IQ scores in offspring in some studies. Newborns also have limited iodine stores and immature kidneys, making them more vulnerable to perchlorate's effects. Infants fed formula using contaminated water may receive higher relative doses of perchlorate than older children or adults.
The EPA established a reference dose for perchlorate of 0.0007 milligrams per kilogram of body weight per day, which was used to derive an informal guideline of 24 parts per billion (ppb) in drinking water. However, this remains a non-enforceable guideline, not a legal standard. Several states, including California, Massachusetts, and Texas, have set their own enforceable standards below the EPA's guidance level.
Current EPA Regulation Status and Why Perchlorate Isn't Yet Regulated
Perchlorate has been a candidate for federal regulation under the Safe Drinking Water Act for many years. In 2011, the EPA determined that perchlorate met the criteria for regulation, meaning it was deemed to pose a meaningful risk to public health. However, despite this determination, perchlorate has not yet become a regulated contaminant with a maximum contaminant level (MCL) that all water utilities must comply with.
The reasons for this delay are complex and involve cost-benefit analysis, political considerations, and the challenge of establishing a regulation that balances public health protection with the economic burden on water utilities. Implementing perchlorate treatment across all affected systems would require significant capital investment in new treatment infrastructure.
In the absence of federal regulation, some states have taken their own action. California set a drinking water standard of 6 ppb in 2007. Massachusetts established a standard of 2 ppb. Texas has guidance of 4 ppb for pregnancy-related advisory purposes. These state standards create a patchwork of protection across the country, leaving residents in unregulated states with less clear guidance about safe levels.
Which Water Supplies Are Affected by Perchlorate?
While approximately 40 water supplies in the United States have detected perchlorate, the actual number of affected communities may be higher because many utilities do not routinely test for it. Here are the regions with the highest documented contamination:
- Nevada: Las Vegas Valley Water District is the most significantly affected system in the nation, with historical perchlorate levels sometimes exceeding 10 ppb. The Colorado River, which supplies much of Las Vegas's water, carries perchlorate contamination originating from upstream sources and manufacturing sites.
- California: Multiple systems in Southern California, particularly those drawing water from the Colorado River or groundwater in agricultural regions, have detected perchlorate. The Los Angeles Department of Water and Power and other systems in the area have documented contamination.
- Texas: Water systems in El Paso and surrounding areas have detected perchlorate, partly due to proximity to military installations and historical manufacturing sites.
- Massachusetts: Several public water supplies, particularly in the northeastern region, have detected perchlorate from historical manufacturing and military activities.
- Florida, New Mexico, and Oklahoma: Various smaller systems and private wells in these states have tested positive for perchlorate.
The problem is that if your water utility isn't required to test for perchlorate and hasn't chosen to do so voluntarily, you likely won't know if it's present in your tap water. This is where taking independent action becomes important.
How to Test Your Drinking Water for Perchlorate
Understanding Why Standard Testing May Not Detect Perchlorate
Most water utilities test for contaminants required by federal and state Safe Drinking Water Act regulations. Since perchlorate is not federally regulated (except in a few states), it is not on the standard testing list for most utilities. This means your water system's annual water quality report, called a Consumer Confidence Report (CCR), may not include any information about perchlorate, even if it is present in your water.
This gap in standard testing is precisely why ClearWater and similar tools were created. By entering your ZIP code on ClearWater's free lookup tool, you can see what contaminants have been detected in your area's water supplies, which may help reveal if perchlorate has been a concern historically in your region, even if it's not regularly reported.
Steps to Get Your Water Tested for Perchlorate
Contact your water utility directly. Call your local water supplier and ask if they test for perchlorate and what their results are. Utilities serving areas with known contamination may already have data available. Request a copy of their most recent perchlorate testing results if available.
Request testing through your state's environmental agency. If your water utility doesn't conduct perchlorate testing, contact your state's environmental or health department. Some states maintain databases of perchlorate testing or can direct you to testing resources.
Hire a certified lab for private testing. If you have a private well or want independent confirmation of your tap water quality, you can hire a certified laboratory to test your water for perchlorate. You'll need to collect water samples according to the lab's instructions and submit them. Contact your state's environmental agency for a list of certified labs in your area that conduct perchlorate analysis. The lab will likely use ion chromatography or mass spectrometry to detect perchlorate at very low concentrations.
Check local health department records. In some cases, local health departments or environmental agencies may have conducted perchlorate testing in your area. Contact your county health department to ask if any testing data exists for your region.
Understanding Perchlorate Test Results
When you receive test results, you'll see perchlorate measured in parts per billion (ppb) or micrograms per liter (mcg/L), which are equivalent units. Here's how to interpret the numbers:
- Below 2 ppb: Generally considered very safe, below all state standards currently in effect.
- 2 to 6 ppb: In the range where different states have set standards. Massachusetts considers this level of concern; California's standard is 6 ppb.
- 6 to 24 ppb: Below the EPA's informal reference level but above some state standards. If you're pregnant, planning pregnancy, or have an infant, treatment should be considered.
- Above 24 ppb: Exceeds the EPA's informal guideline. Treatment is recommended for all populations, especially vulnerable groups.
Removal and Treatment Methods for Perchlorate
Ion Exchange Treatment
Ion exchange is one of the most effective treatment methods for removing perchlorate from drinking water at both municipal and household levels. This process uses specially designed resins that attract and bind perchlorate ions, removing them from the water as it passes through the treatment system.
Ion exchange systems designed specifically for perchlorate removal are highly effective, often removing 95 percent or more of perchlorate from contaminated water. The main consideration is that these resins require regeneration after they become saturated with perchlorate, a process that produces a waste stream containing concentrated perchlorate that must be properly disposed of.
For households, ion exchange can be installed as a point-of-use system (treating water at a single tap) or point-of-entry system (treating all water entering the home). Point-of-entry systems offer broader protection but are more expensive and require professional installation and ongoing maintenance.
Reverse Osmosis Filtration
Reverse osmosis (RO) is another highly effective method for removing perchlorate from drinking water. In this process, water is forced through a semi-permeable membrane under pressure. Perchlorate ions and most other contaminants are too large to pass through the membrane and are removed from the water.
Reverse osmosis systems can remove 90 to 99 percent of perchlorate, depending on the system and its condition. These systems are commonly available as point-of-use units that can be installed under a kitchen sink or as countertop models. They are relatively affordable for household use compared to whole-home treatment systems.
The downside of reverse osmosis is that it produces wastewater (called reject water or brine) that is discharged down the drain. For every gallon of purified water produced, several gallons of wastewater may be generated, depending on the system. Some newer RO systems have improved efficiency and waste less water.
Other Treatment Considerations
Standard activated carbon filters, commonly found in pitcher filters and basic faucet filters, do not effectively remove perchlorate. If you currently rely on these for water filtration, be aware that perchlorate will pass through.
Boiling water does not remove perchlorate and may actually increase its concentration slightly as water evaporates. Distillation can remove perchlorate but is not practical for large-scale home water treatment.
Municipal water systems facing perchlorate contamination typically use ion exchange treatment at the facility level. Some systems blend contaminated groundwater with cleaner surface water sources to dilute perchlorate concentrations below health-based guidance levels.
Steps to Protect Yourself and Your Family from Perchlorate
- Determine if perchlorate is in your water supply. Check ClearWater's free tool by entering your ZIP code to see if perchlorate has been detected in your area. Contact your water utility to ask if they test for perchlorate and request results.
- Assess your risk level. If you are pregnant, planning pregnancy, have an infant, or have existing thyroid disease, your risk from perchlorate exposure is higher. Consider testing your water or implementing treatment even if perchlorate levels are in the lower range.
- Conduct testing if recommended. If your water utility doesn't test for perchlorate and you live in an area where it might be present, hire a certified lab to test your water.
- Implement treatment if needed. If testing reveals perchlorate in your water above 2 ppb, consider installing either a reverse osmosis system or ion exchange treatment. Point-of-use systems under your kitchen sink can protect your drinking and cooking water without major expense or installation.
- Stay informed. Keep checking with your water utility and state environmental agency for updates on perchlorate regulation and any new requirements for testing or treatment in your area.
- Ensure adequate iodine intake. While not a substitute for removing perchlorate from water, maintaining adequate iodine intake through diet (iodized salt, dairy, seafood) helps your thyroid maintain normal function even with modest perchlorate exposure.
- Maintain your treatment system. If you install a water filtration or treatment system, follow the manufacturer's maintenance schedule. Filters and resins need replacement at regular intervals to remain effective.
What the Future Holds for Perchlorate Regulation
The EPA continues to evaluate perchlorate for federal regulation. Environmental groups and public health advocates have urged the agency to establish a maximum contaminant level that would require all water utilities to test for and treat perchlorate. The delay in federal regulation has frustrated many public health experts who believe the evidence of harm, particularly to infants and pregnant women, is sufficient to warrant mandatory controls.
In the meantime, continued state-level action and public pressure may drive more utilities to voluntarily test for and treat perchlorate even without federal requirements. As testing becomes more common and results are shared publicly, awareness of perchlorate contamination will likely increase, particularly in affected communities.
For now, the responsibility largely falls on individual homeowners to determine whether perchlorate is a concern in their water supply and to take steps to protect themselves. By using available tools like ClearWater and taking direct action to test and treat your water when necessary, you can reduce your family's exposure to this persistent and concerning contaminant.