Disinfection byproducts
Perchlorate in U.S. tap water
46 public water systems across 7 U.S. states report Perchlorate in their annual Consumer Confidence Report. None currently sit at or above the federal limit.
What it is
A chemical used in rocket fuel and fireworks that can also form during disinfection.
Why it's regulated
Can interfere with thyroid hormone production; has no national enforceable limit but is regulated in some states.
Within the federal limit (28)
| Water system | Measured |
|---|---|
| Pomona, CA 2024 annual report | 0–3.5 ug/L |
| Glendale, CA 2024 annual report | 2.4 ug/L |
| City of Hemet, CA 2024 annual report | 2.3 ug/L |
| City of Menifee, CA 2024 annual report | 2.3 ug/L |
| City of Murrieta, CA 2024 annual report | 2.3 ug/L |
| City of Perris, CA 2024 annual report | 2.3 ug/L |
| City of San Jacinto, CA 2024 annual report | 2.3 ug/L |
| City of Temecula, CA 2024 annual report | 2.3 ug/L |
| East Valley Service Area, CA 2024 annual report | 2.3 ug/L |
| Mills Service Area, CA 2024 annual report | 2.3 ug/L |
| Moreno Valley, CA 2024 annual report | 2.3 ug/L |
| Skinner Service Area, CA 2024 annual report | 2.3 ug/L |
| Bakersfield, CA 2024 annual report | 2 mg/L |
| Riverside, CA 2024 annual report | 2 |
| Ontario, CA 2024 annual report | 1.5 ug/L |
| Pasadena, CA 2023 annual report | 1.3 ug/L |
| Santa Ana, CA 2024 annual report | 1.2 ug/L |
| Rancho Cucamonga, CA 2024 annual report | 0.86 ug/L |
| Fontana, CA 2024 annual report | 0.1 ug/L |
| Brockton, MA 2024 annual report | 0.13 ug/L |
| Charleston, SC 2024 annual report | 0.44 ug/L |
| North Charleston, SC 2024 annual report | 0.44 ug/L |
| Charlotte, NC 2024 annual report | 0.07 ug/L |
| Chico, CA 2024 annual report | Not detected ug/L |
| Fullerton, CA 2024 annual report | Not detected ug/L |
| Rialto, CA 2024 annual report | Not detected ug/L |
| San Francisco SFPUC, CA 2023 annual report | Not detected ug/L |
| Santa Clara, CA 2024 annual report | Not detected ug/L |
Frequently asked
+What is Perchlorate?
A chemical used in rocket fuel and fireworks that can also form during disinfection. Can interfere with thyroid hormone production; has no national enforceable limit but is regulated in some states.
+What is the federal limit for Perchlorate in drinking water?
The federal MCL for Perchlorate is 6 mg/L. The EPA enforces this against the regulated reporting statistic (typically a running annual average or 90th percentile), not a single-sample spike.
+How many U.S. water systems have Perchlorate over the federal limit?
Zero of the 46 public water systems in The Water Map dataset currently report Perchlorate at or above its federal limit.
+How can I check if Perchlorate is in my city's tap water?
Search your city on The Water Map (https://www.thewatermap.com/) or browse the list on this page. Every U.S. public water utility is required to publish an annual Consumer Confidence Report that lists every contaminant it measured, including Perchlorate.