Perchlorate is a rocket fuel component and natural mineral salt detected in groundwater and drinking water across Southern California, particularly in the Inland Empire counties of San Bernardino and Riverside. California established an enforceable Maximum Contaminant Level of 6 parts per billion for perchlorate in drinking water, enforced by the State Water Resources Control Board. California's Office of Environmental Health Hazard Assessment set a public health goal of 1 ppb, six times lower than the legal limit, based on thyroid hormone disruption risk. Industrial use of ammonium perchlorate by aerospace and defense contractors in the San Gabriel Valley and Inland Empire throughout the mid-to-late twentieth century is the primary driver of groundwater contamination in the region. This article maps what utility Consumer Confidence Reports and EPA monitoring data show county by county, and explains which treatment technologies the evidence supports.
Published August 15, 2026 · Data sourced from public regulatory filings · Southern California Water Treatment
California regulates perchlorate at 6 ppb, with a public health goal of 1 ppb
California was one of the first states to adopt an enforceable MCL for perchlorate in drinking water. The State Water Resources Control Board requires all regulated utilities to test and report perchlorate levels annually. For context on this and other regulated contaminants, the California MCLs and PHGs table at waterboards.ca.gov lists every regulated substance with its enforceable limit and corresponding health goal side by side.
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What is perchlorate and why is it in Southern California water?
Perchlorate is a chemical compound that occurs both naturally and as a result of industrial activity. In its naturally occurring form, it forms through atmospheric and chemical processes in arid, high-altitude environments, which is why it appears at background levels in the Colorado River, a primary source of imported water for much of Southern California. At those background concentrations, detections are typically low and managed through standard water treatment at metropolitan level.
The more significant contamination concern in Southern California is industrial in origin. Ammonium perchlorate is the oxidizer compound used in solid rocket propellant. Throughout the Cold War and into the late twentieth century, aerospace and defense contractors in Los Angeles, San Bernardino, and Riverside counties manufactured, stored, and disposed of large quantities of ammonium perchlorate. Spills, leaks, and improper disposal at facilities in Burbank, El Monte, Azusa, Baldwin Park, Rialto, and other industrial corridors resulted in groundwater plumes that persist today because perchlorate is highly soluble and does not readily break down in the subsurface environment.
The Rialto Groundwater Plume in San Bernardino County is one of the best-documented examples. Listed as an EPA Superfund site, the plume has required extensive groundwater monitoring and remediation by responsible parties over many years. Similar legacy contamination zones exist in the San Gabriel Valley, where the San Gabriel Basin Water Quality Authority coordinates groundwater protection across multiple overlapping plumes from aerospace-era operations.
For homeowners on well water in Riverside County or other parts of the Riverside County service area and San Bernardino County service area, understanding perchlorate risk requires looking at what your specific groundwater basin shows, not just regional averages. Water from a municipal utility drawing on affected groundwater may test differently than a private well a mile away.
Which Southern California counties show perchlorate detections?
Perchlorate monitoring results vary substantially by county depending on water source mix, treatment infrastructure, and proximity to historical contamination sites. The table below summarizes what utility Consumer Confidence Reports and California State Water Resources Control Board monitoring records show for each of the seven Southern California counties. All data reflects publicly filed regulatory reports; this is not an endorsement or condemnation of any specific utility. Verify current levels for your utility using the sources listed in the FAQ section at the bottom of this article.
| County | Key Utility / Source | Perchlorate Status (Treated Tap) | Primary Driver | Source |
|---|---|---|---|---|
| San Bernardino (Inland Empire) | Inland Empire Utilities Agency / West Valley Water District | Detections documented in select groundwater wells; utility monitoring ongoing | Aerospace and defense industry ammonium perchlorate use; Rialto Groundwater Plume (EPA CERCLA) | IEUA 2023 to 2024 CCR; EPA CERCLA site records; CA SWRCB Drinking Water Watch |
| Riverside | Western Municipal Water District / Elsinore Valley MWD | Trace detections in some groundwater sources; well within 6 ppb MCL at treated tap | Historical military rocket testing activity; Colorado River source water influence | Western MWD 2023 CCR; CA SWRCB raw monitoring data |
| Los Angeles | LADWP / San Gabriel Valley MWD | Below detection limits in most LADWP surface water; San Gabriel Basin wells have historical detections | San Gabriel Valley Superfund complex; aerospace legacy sites in El Monte, Azusa, Baldwin Park corridors | LADWP 2023 Consumer Confidence Report; EPA UCMR data; San Gabriel Basin Water Quality Authority reports |
| Orange | Orange County Water District | Generally below detection limits in treated water; OCWD advanced purification removes trace levels | OCWD Groundwater Replenishment System provides treatment barrier; primarily surface water sourced | OCWD 2024 Water Quality Report; EWG Tap Water Database |
| San Diego | San Diego County Water Authority | Minimal detections; SDCWA purchases primarily treated Metropolitan Water District supply | Colorado River supply via MWD; perchlorate levels low in treated imported water | SDCWA 2024 Water Quality Report; MWD Water Quality Report 2024 |
| Ventura | Calleguas Municipal Water District | Trace levels consistent with MWD imported supply; no exceedances reported | Relies on Metropolitan Water District imports and local groundwater; limited industrial history | Calleguas MWD 2023 CCR; MWD Water Quality Report 2024 |
Sources: Utility Consumer Confidence Reports 2023 to 2024; California State Water Resources Control Board Drinking Water Program (waterboards.ca.gov); EPA Safe Drinking Water Information System (sdwis.epa.gov).
What is California's legal limit for perchlorate in drinking water?
California established a Maximum Contaminant Level for perchlorate of 6 parts per billion (ppb), administered by the State Water Resources Control Board under the California Safe Drinking Water Act. This makes California one of the first states in the nation to adopt an enforceable standard for this compound. The full regulatory details are published at waterboards.ca.gov/drinking_water/certlic/drinkingwater/Perchlorate.html.
Separately, California's Office of Environmental Health Hazard Assessment (OEHHA) set a public health goal (PHG) of 1 ppb for perchlorate, based on a no-observed-adverse-effect level for thyroid iodide uptake inhibition. The PHG is a health-based target, not an enforceable limit, and is detailed at oehha.ca.gov/chemicals/perchlorate. The six-fold gap between the health goal (1 ppb) and the enforceable MCL (6 ppb) is significant for households with pregnant women, infants, or individuals managing thyroid conditions, for whom even sub-MCL levels may warrant a treatment conversation with a physician.
At the federal level, the EPA has authority over perchlorate under the Safe Drinking Water Act and has published regulatory guidance at epa.gov/sdwa/perchlorate-drinking-water. Because California's state standard preceded federal action, regulated California utilities have been subject to the 6 ppb limit regardless of any changes in federal regulatory posture. The California standard applies to all public water systems serving more than 200 connections.
For comparison, other SoCal contaminants with similar regulatory structure include chromium-6, which has a California MCL of 10 ppb and an OEHHA public health goal of 0.02 ppb, and arsenic, which has a federal MCL of 10 ppb and a California public health goal of 4 ppt. In each case, the health goal is substantially lower than the enforceable limit. Our Southern California water quality by county guide covers these contaminants together.
How does perchlorate affect health?
Perchlorate's primary mechanism of harm is competitive inhibition of iodide transport into the thyroid gland. The thyroid takes up iodide from the bloodstream to synthesize thyroid hormone. Perchlorate competes for the same transporter, reducing the iodide available to the gland and potentially lowering thyroid hormone production at sufficiently high exposures or in individuals with already marginal iodide intake.
California's OEHHA established the 1 ppb public health goal after evaluating studies of thyroid iodide uptake inhibition in adults and applying protective factors for sensitive populations. The full risk assessment is available at oehha.ca.gov/chemicals/perchlorate. Populations considered more sensitive include pregnant women, because thyroid hormone is critical for fetal neurological development; infants consuming formula prepared with tap water; individuals with pre-existing hypothyroidism or iodine deficiency; and people on low-iodine diets.
For the general adult population without thyroid conditions, perchlorate at levels below the 6 ppb MCL is not expected to cause acute health effects. The concern is chronic, low-level exposure over time. The degree of risk depends on total perchlorate intake from all sources, including food, particularly leafy vegetables grown with contaminated irrigation water, which can concentrate the compound.
Perchlorate is not the only thyroid-relevant contaminant in SoCal water. Nitrate also interferes with iodide metabolism at high concentrations, and chlorination byproducts present separate concerns for long-term exposure. A whole-home filtration system addresses multiple compound classes simultaneously.
Concerned about perchlorate specifically?
Our licensed technicians size reverse osmosis systems and whole-home filtration based on a real water test at your address, not a regional estimate. Our 90-day satisfaction guarantee and 5-year warranty cover all installations.
What filter removes perchlorate from tap water?
Two treatment technologies have documented effectiveness against perchlorate at concentrations typical of Southern California municipal supplies:
Reverse osmosis (NSF/ANSI Standard 58)
RO systems certified to NSF/ANSI 58 are independently tested for perchlorate reduction. The membrane rejects perchlorate ions along with most dissolved inorganic compounds, with removal rates typically documented at 90 to 95 percent in independent testing. For drinking water at the point of use (under-sink or countertop), a certified RO system is the most direct solution. Our reverse osmosis installation service covers sizing, permitting, and same-day installation across Los Angeles, Orange, San Diego, Riverside, San Bernardino, and Ventura counties.
Strong-base anion exchange resin
Ion exchange systems using strong-base anion resin selectively bind perchlorate, removing it from the water stream with high efficiency. This approach is used both at point-of-use scale and in larger whole-home systems. It is the technology used by several California utilities for groundwater remediation in affected basins. Resin regeneration or replacement is required periodically based on influent concentration and water volume treated.
What does NOT remove perchlorate
Standard activated carbon filters, including pitcher filters and refrigerator filters certified to NSF/ANSI 42 or NSF/ANSI 53, are not certified for perchlorate removal and should not be relied on for this contaminant. Carbon filtration addresses chlorine taste and odor, some volatile organic compounds, and select other contaminants, but perchlorate does not adsorb to carbon effectively. Check any filter's certification at the NSF certified product search to confirm what it actually removes.
For the Inland Empire specifically, where well water users face the highest uncertainty about perchlorate levels, the right starting point is an in-home water test, not a regional estimate. Our PFAS and contaminant filter guide for Riverside County covers a broader set of contaminants relevant to that service area, including perchlorate and PFAS compounds that sometimes co-occur at industrial-legacy sites.
A combo hybrid whole-home system combining pre-filtration, a softener stage, and an RO drinking water stage addresses perchlorate at the point of use while also managing the hard water (18 to 30 grains per gallon across most SoCal counties) that accelerates scale buildup on plumbing and appliances. Our Southern California water hardness guide covers the hardness picture county by county.
How does perchlorate compare to other regulated SoCal water contaminants?
Southern California homeowners considering water treatment often encounter multiple contaminant concerns simultaneously. Perchlorate sits alongside several other regulated compounds in the SoCal water quality picture, each with its own source, health mechanism, and treatment approach.
Chromium-6 (hexavalent chromium)
California MCL: 10 ppb. OEHHA PHG: 0.02 ppb. Detectable in all seven SoCal counties. Requires zero-valent iron reduction or strong-base anion exchange for removal, not standard carbon. Our chromium-6 SoCal guide covers the county-by-county picture.
Federal MCL: 10 ppb. California PHG: 4 ppt. Elevated in Inland Empire and Imperial Valley well water. Reverse osmosis and adsorptive iron media remove it effectively. See our arsenic in Southern California water guide.
Federal MCL: 10 ppm. Agricultural-legacy contamination in Orange County and Ventura County well water. Critical concern for infant formula preparation. Reverse osmosis removes it effectively. See our nitrates in Southern California water guide.
EPA MCLs now established at 4 ppt for PFOA and PFOS. Detected in SoCal military base and industrial corridor groundwater. Granular activated carbon and high-rejection RO membranes provide removal.
Not a regulated health contaminant, but 18 to 30 grains per gallon across most SoCal counties causes measurable scale accumulation and reduces appliance efficiency. Our water softener installation service addresses hardness at the whole-home level.
The reason a combination approach, such as a whole-home filtration system paired with an under-sink reverse osmosis unit for drinking water, is common among Inland Empire homeowners is that no single contaminant exists in isolation. An RO stage handles perchlorate, nitrate, arsenic, chromium-6, and PFAS at the drinking tap simultaneously while a pre-filter and softener stage protects plumbing and appliances from scale and sediment.
How do I find the perchlorate level for my specific water utility?
Three public sources carry utility-level perchlorate monitoring data for Southern California:
- Your utility's annual Consumer Confidence Report (CCR). Every regulated public water system in California is required by the EPA Safe Drinking Water Act to publish an annual CCR listing detected contaminants and their measured levels relative to the MCL. Search your utility's name plus "Consumer Confidence Report 2024" to find it. The CCR covers perchlorate if the utility detected it at any level above the minimum reporting threshold.
- California Drinking Water Watch at waterboards.ca.gov. The State Water Resources Control Board maintains a publicly searchable database of raw monitoring results by public water system ID. This database includes both current and historical perchlorate test results, which is useful for understanding trends over time. waterboards.ca.gov/drinking_water.
- EPA Safe Drinking Water Information System (SDWIS) at sdwis.epa.gov. The federal system carries monitoring records for all utilities regulated under the Safe Drinking Water Act. Useful for cross-referencing California data and for utilities operating near county lines. sdwis.epa.gov.
For well water users not served by a regulated utility, no public database covers your specific well. A certified laboratory water test is the only way to know your perchlorate level. We offer a free in-home water test that screens for the primary SoCal contaminants of concern. Book through our contact page or use the water checker tool to see what is typical for your county.
If you are on a private well in the Inland Empire, Riverside County, or rural parts of Los Angeles County, the EPA recommends testing annually for regulated contaminants including perchlorate, nitrate, arsenic, and coliform bacteria. See the EPA Safe Drinking Water Information System at epa.gov/sdwa for guidance on private well testing requirements by state.
What Southern California homeowners should do next
Perchlorate risk in Southern California is geographically concentrated in the Inland Empire and parts of the San Gabriel Valley, but trace detections appear in other counties due to Colorado River source water contributions. The action steps depend on your location and water source:
If you are on a municipal supply in San Bernardino or Riverside County
Pull your utility's most recent Consumer Confidence Report and check the perchlorate row. If the detected level is above 1 ppb (the OEHHA public health goal) and you have pregnant household members, infants, or anyone with a thyroid condition, consider an NSF/ANSI 58-certified reverse osmosis system for drinking and cooking water.
If you are on a private well in the Inland Empire
Commission a certified laboratory test for perchlorate, arsenic, nitrate, and coliform bacteria. Do not rely on a neighbor's test result or a regional average. Well water chemistry varies significantly even within the same aquifer zone. We can facilitate testing and interpret results in the context of appropriate treatment options.
If you are in Los Angeles, Orange, San Diego, or Ventura County
Perchlorate is less likely to be a primary concern at your tap, but chromium-6, PFAS, hard water, and disinfection byproducts remain relevant. The SoCal water quality by county guide covers the full picture for each county, and our FAQ answers common questions about SoCal water treatment options.
Frequently asked questions about perchlorate in SoCal water
What is the legal limit for perchlorate in California drinking water?
California established a Maximum Contaminant Level (MCL) for perchlorate of 6 parts per billion (ppb), making it one of the first states in the nation to regulate the compound in drinking water. This MCL is enforced by the California State Water Resources Control Board. California's public health goal, set separately by the Office of Environmental Health Hazard Assessment, is 1 ppb, six times lower than the enforceable limit. Source: waterboards.ca.gov/drinking_water.
Why does the Inland Empire have higher perchlorate risk than coastal Southern California?
The Inland Empire draws a larger share of its supply from local groundwater rather than imported surface water, and the San Bernardino County industrial corridor has documented historical use of ammonium perchlorate by aerospace and defense contractors. The Rialto Groundwater Plume, listed as an EPA Superfund site, is a primary contamination source in the region. Coastal utilities relying on Metropolitan Water District imports generally receive treated water with much lower perchlorate concentrations.
Does reverse osmosis remove perchlorate from drinking water?
Yes. Reverse osmosis systems certified to NSF/ANSI Standard 58 are tested for perchlorate reduction. Independent testing documents 90 to 95 percent removal rates at concentrations typical of California municipal supplies. Ion exchange systems using strong-base anion resin also remove perchlorate with high efficiency. Standard activated carbon filters are not certified for perchlorate removal and should not be relied on for this contaminant.
Is perchlorate dangerous at levels found in SoCal tap water?
The health concern with perchlorate is thyroid disruption. Perchlorate competes with iodide for uptake by the thyroid gland, potentially reducing thyroid hormone production. California's OEHHA set the public health goal at 1 ppb based on a no-observed-adverse-effect level for thyroid inhibition. Pregnant women, infants, and people with thyroid conditions are considered more sensitive. Most SoCal utilities report treated water below the 6 ppb MCL, but the gap between the legal limit and the health goal is meaningful for at-risk individuals.
Where does perchlorate in Southern California water come from?
Two primary sources are documented in Southern California. Industrial contamination: ammonium perchlorate is the oxidizer in solid rocket fuel, and aerospace and defense manufacturing in the San Gabriel Valley, Inland Empire, and other SoCal industrial corridors released it into groundwater over decades. Natural sources: perchlorates also form naturally in arid environments through atmospheric deposition, contributing low background levels throughout the Colorado River watershed, which supplies a significant portion of Southern California's imported water.
How do I find the perchlorate level in my specific water utility?
Three public sources carry utility-level data. First, your utility's annual Consumer Confidence Report, required under the EPA Safe Drinking Water Act, lists contaminants detected and their measured levels. Second, the California State Water Resources Control Board's Drinking Water Watch portal at waterboards.ca.gov allows searches by public water system ID. Third, the EPA's Safe Drinking Water Information System (SDWIS) at sdwis.epa.gov holds federal monitoring records for regulated utilities.
Related reading
- Chromium-6 in Southern California Water: 2024 state testing across 7 counties
- Arsenic in Southern California water: Inland Empire and Imperial Valley data
- Nitrates in Southern California water: agricultural-legacy contamination guide
- PFAS forever chemicals in Southern California: utility detections and filter options
- PFAS water filter guide for Riverside County homeowners
- Water hardness in Southern California: county-by-county data and softener guide
- Southern California water quality by county 2026: chromium-6, hardness, arsenic, perchlorate
Service areas where we install perchlorate-rated systems
We serve all seven Southern California counties. County-specific water quality context and service details:
