Thousand Oaks, California Tap Water Quality Report
Serving utility: Calleguas Municipal Water District
Updated March 2026 • Data from EWG Tap Water Database & EPA SDWIS
High Priority Concerns
Thousand Oaks tap water has 15 contaminants exceeding EWG health guidelines, including Haloacetic acids (HAA5), Arsenic, Radon. Additionally, 14 known or suspected carcinogens were detected, including Haloacetic acids (HAA5), Arsenic, Total trihalomethanes (TTHMs).
Water Provider Information
Contaminants Detected
| Contaminant | Detected Level | EWG Guideline | Legal Limit | Status |
|---|---|---|---|---|
| Haloacetic acids (HAA5) carcinogen | 36.20 ppb | 0.10 ppb | 60 ppb | Above guideline |
| Arsenic carcinogen | 1.10 ppb | 0.00 ppb | 10 ppb | Above guideline |
| Radon | 258.72 pCi/L | 1.50 pCi/L | No legal limit | Above guideline |
| Dibromoacetic acid | 4.74 ppb | 0.03 ppb | No legal limit | Above guideline |
| Total trihalomethanes (TTHMs) carcinogen | 23 ppb | 0.15 ppb | 80 ppb | Above guideline |
| Dibromochloromethane carcinogen | 8.47 ppb | 0.10 ppb | No legal limit | Above guideline |
| Bromodichloromethane carcinogen | 3.97 ppb | 0.06 ppb | No legal limit | Above guideline |
| Bromoform carcinogen | 8.87 ppb | 0.50 ppb | No legal limit | Above guideline |
| Dichloroacetic acid carcinogen | 3.09 ppb | 0.20 ppb | No legal limit | Above guideline |
| Bromochloromethane | 0.70 ppb | 0.06 ppb | No legal limit | Above guideline |
| Trichloroacetic acid carcinogen | 0.75 ppb | 0.10 ppb | No legal limit | Above guideline |
| Chloroform carcinogen | 1.68 ppb | 0.40 ppb | No legal limit | Above guideline |
| Uranium carcinogen | 1.09 pCi/L | 0.43 pCi/L | 20 pCi/L | Above guideline |
| Nitrate carcinogen | 0.17 ppm | 0.14 ppm | 10 ppm | Above guideline |
| Nitrate and nitrite carcinogen | 0.16 ppm | 0.14 ppm | 10 ppm | Above guideline |
| Dibromomethane | 1.33 ppb | N/A | No legal limit | Below guideline |
| Dichloromethane (methylene chloride) carcinogen | 0.32 ppb | 4 ppb | 5 ppb | Below guideline |
| Fluoride | 0.63 ppm | N/A | 4 ppm | Below guideline |
| Manganese | 31.50 ppb | 100 ppb | No legal limit | Below guideline |
| Monobromoacetic acid | 0.94 ppb | 25 ppb | No legal limit | Below guideline |
| Monochloroacetic acid | 1.07 ppb | 53 ppb | No legal limit | Below guideline |
| Nitrite carcinogen | 0.01 ppm | N/A | 1 ppm | Below guideline |
| Selenium | 2.65 ppb | 30 ppb | 50 ppb | Below guideline |
| Vanadium | 0.64 ppb | 21 ppb | No legal limit | Below guideline |
| Xylenes (total) | 0.03 ppb | 1,800 ppb | 10,000 ppb | Below guideline |
Health Context
Haloacetic acids (HAA5) carcinogen
Exposure to elevated levels of this contaminant may pose health risks. See EWG and EPA guidelines for more information.
Arsenic carcinogen
Long-term exposure increases risk of skin cancer, bladder cancer, and lung cancer; chronic exposure causes neurological effects and cardiovascular disease.
Radon
Radon is a radioactive gas that accumulates in lungs over time, significantly increasing lung cancer risk, particularly in smokers and former smokers with prolonged exposure.
Dibromoacetic acid
Exposure to elevated levels of this contaminant may pose health risks. See EWG and EPA guidelines for more information.
Total trihalomethanes (TTHMs) carcinogen
Exposure to elevated levels of this contaminant may pose health risks. See EWG and EPA guidelines for more information.
Recommended Filtration for This Water
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Shop Hydrogen FlaskFrequently Asked Questions
Is Thousand Oaks tap water safe to drink?
Thousand Oaks tap water meets EPA legal standards for drinking water. However, 15 contaminants exceed stricter EWG health guidelines, and 14 known carcinogens were detected. While legally compliant, additional filtration is recommended for optimal safety.
What contaminants are in Thousand Oaks water?
A total of 25 contaminants were detected in Thousand Oaks tap water, including Haloacetic acids (HAA5), Arsenic. Of these, 15 exceed EWG health guidelines.
What's the best water filter for Thousand Oaks?
For Thousand Oaks tap water, we recommend a reverse osmosis (RO) system for drinking water — it removes up to 99.9% of contaminants including heavy metals, PFAS, and disinfection byproducts. For shower and bath water, a whole-home filtration system reduces chlorine and volatile organics.
Where does Thousand Oaks get its water?
Thousand Oaks tap water is provided by Calleguas Municipal Water District, serving approximately 640,000 people. For detailed source water information, contact your local utility or visit the EPA's SDWIS database.
Nearby City Water Reports
Data sources: Environmental Working Group (EWG) Tap Water Database, U.S. EPA Safe Drinking Water Information System (SDWIS)
Last updated: March 2026
Methodology: Contaminant levels are compared against both EPA legal limits (Maximum Contaminant Levels) and EWG health guidelines, which are often stricter and based on the latest scientific research.
