Disinfection byproducts
TTHM in U.S. tap water
395 public water systems across 45 U.S. states report TTHM in their annual Consumer Confidence Report. 28 sit at or above the federal limit.
395
systems measuring
28
over the limit
45
states represented
What it is
Total trihalomethanes — a group of four chemicals (including chloroform) formed when chlorine reacts with natural organic matter.
Why it's regulated
Long-term exposure above the federal limit is linked to liver, kidney, and central-nervous-system effects and increased cancer risk.
Federal limit0.08 mg/L· MCL
At or above the federal limit (28)
| Water system | Measured | vs. limit |
|---|---|---|
| Albuquerque, NM 2024 annual report | 38.8 | 77.6× the limit |
| City of Hemet, CA 2024 annual report | 16–67 ug/L | 67.0× the limit |
| City of Menifee, CA 2024 annual report | 16–67 ug/L | 67.0× the limit |
| City of Murrieta, CA 2024 annual report | 16–67 ug/L | 67.0× the limit |
| City of Perris, CA 2024 annual report | 16–67 ug/L | 67.0× the limit |
| City of San Jacinto, CA 2024 annual report | 16–67 ug/L | 67.0× the limit |
| City of Temecula, CA 2024 annual report | 16–67 ug/L | 67.0× the limit |
| East Valley Service Area, CA 2024 annual report | 16–67 ug/L | 67.0× the limit |
| Mills Service Area, CA 2024 annual report | 16–67 ug/L | 67.0× the limit |
| Moreno Valley, CA 2024 annual report | 16–67 ug/L | 67.0× the limit |
| Skinner Service Area, CA 2024 annual report | 16–67 ug/L | 67.0× the limit |
| Ontario, CA 2024 annual report | 50 ug/L | 50.0× the limit |
| Columbus, OH 2025 annual report | 2025 ug/L | 25.3× the limit |
| Hollywood, FL 2024 annual report | 2024 ug/L | 25.3× the limit |
| Mcallen, TX 2024 annual report | 2024 ug/L | 25.3× the limit |
| Pittsburgh, PA 2024 annual report | 17–119 ug/L | 1.5× the limit |
| Freedom District, MD 2024 annual report | 21.3–114.3 ug/L | 1.4× the limit |
| High Point, NC 2024 annual report | 111 ug/L | 1.4× the limit |
| Goodyear, AZ 2024 annual report | 104 ug/L | 1.3× the limit |
| Akron, OH 2024 annual report | 32.4–98.3 ug/L | 1.2× the limit |
| Atlanta, GA 2024 annual report | 14.4–95.8 ug/L | 1.2× the limit |
| Brunswick, MD 2024 annual report | 24.62–92.76 ug/L | 1.2× the limit |
| Jacksonville, FL 2024 annual report | 25.71–91.49 ug/L | 1.1× the limit |
| Billings, MT 2024 annual report | 17–91 ug/L | 1.1× the limit |
| West Palm Beach, FL 2024 annual report | 13.9–90.1 ug/L | 1.1× the limit |
| Chula Vista Sweetwater, CA 2024 annual report | 4.6–85.46 ug/L | 1.1× the limit |
| Keswick Multi Care Center, MD 2024 annual report | 68–85.4 ug/L | 1.1× the limit |
| Columbus, GA 2024 annual report | 23–83 | 1.0× the limit |
Approaching the limit (36)
| Water system | Measured | vs. limit |
|---|---|---|
| Springfield, MA 2024 annual report | 49–78 ug/L | 1.0× the limit |
| City of Cupertino, CA 2024 annual report | 76.96 ug/L | 1.0× the limit |
| San Jose, CA 2024 annual report | 76.96 ug/L | 1.0× the limit |
| Fayetteville, AR 2024 annual report | 12–74.2 ug/L | 0.9× the limit |
| Tulsa, OK 2024 annual report | 74 ug/L | 0.9× the limit |
| Orlando, FL 2024 annual report | 18.87–73.85 ug/L | 0.9× the limit |
| City of Alpharetta, GA 2024 annual report | 73.2 ug/L | 0.9× the limit |
| City of Milton, GA 2024 annual report | 73.2 ug/L | 0.9× the limit |
| City of Roswell, GA 2024 annual report | 73.2 ug/L | 0.9× the limit |
| Johns Creek, GA 2024 annual report | 73.2 ug/L | 0.9× the limit |
| Sandy Springs, GA 2024 annual report | 73.2 ug/L | 0.9× the limit |
| City of Baltimore, MD 2024 annual report | 72 | 0.9× the limit |
| Edmond, OK 2024 annual report | 72 ug/L | 0.9× the limit |
| Providence, RI 2025 annual report | 27.7–71.5 ug/L | 0.9× the limit |
| City of Hialeah, FL 2023 annual report | 51–71 ug/L | 0.9× the limit |
| City of Homestead, FL 2023 annual report | 51–71 ug/L | 0.9× the limit |
| City of North Miami Beach, FL 2023 annual report | 51–71 ug/L | 0.9× the limit |
| Miami Dade, FL 2023 annual report | 51–71 ug/L | 0.9× the limit |
| Grand Rapids, MI 2025 annual report | 70.7 ug/L | 0.9× the limit |
| Oklahoma City, OK 2024 annual report | 69 ug/L | 0.9× the limit |
| Rockville, MD 2024 annual report | 69 ug/L | 0.9× the limit |
| Brockton, MA 2024 annual report | 17–68 ug/L | 0.8× the limit |
| Columbia, SC 2024 annual report | 15–67 | 0.8× the limit |
| Suffolk, VA 2024 annual report | 67 ug/L | 0.8× the limit |
| Mobile, AL 2024 annual report | 8.02–66.85 | 0.8× the limit |
| Henderson, NV 2024 annual report | 66 ug/L | 0.8× the limit |
| Chandler, AZ 2024 annual report | 65 ug/L | 0.8× the limit |
| Gainesville, FL 2024 annual report | 34.3–64.9 ug/L | 0.8× the limit |
| Yonkers, NY 2024 annual report | 25.2–64.7 ug/L | 0.8× the limit |
| Lakeland, FL 2024 annual report | 18.5–64.4 ug/L | 0.8× the limit |
| San Diego, CA 2023 annual report | 8.2–64.1 ug/L | 0.8× the limit |
| Amarillo, TX 2024 annual report | 64 ug/L | 0.8× the limit |
| Bakersfield, CA 2024 annual report | 64 ug/L | 0.8× the limit |
| Bridgeport, CT 2024 annual report | 64 ug/L | 0.8× the limit |
| Broken Arrow, OK 2024 annual report | 64 ug/L | 0.8× the limit |
| Charlotte, NC 2024 annual report | 64 ug/L | 0.8× the limit |
Within the federal limit (280)
| Water system | Measured |
|---|---|
| Ansonia, CT 2024 annual report | 35–63.8 |
| Bethany, CT 2024 annual report | 35–63.8 |
| Branford, CT 2024 annual report | 35–63.8 |
| Cheshire, CT 2024 annual report | 35–63.8 |
| Derby, CT 2024 annual report | 35–63.8 |
| East Haven, CT 2024 annual report | 35–63.8 |
| Hamden, CT 2024 annual report | 35–63.8 |
| Milford, CT 2024 annual report | 35–63.8 |
| New Haven, CT 2024 annual report | 35–63.8 |
| North Haven, CT 2024 annual report | 35–63.8 |
| Orange, CT 2024 annual report | 35–63.8 |
| Seymour, CT 2024 annual report | 35–63.8 |
| West Haven, CT 2024 annual report | 35–63.8 |
| Woodbridge, CT 2024 annual report | 35–63.8 |
| Naperville, IL 2024 annual report | 16.8–63.2 ug/L |
| Vallejo, CA 2024 annual report | 63 ug/L |
| Palm Bay, FL 2024 annual report | 0–62.85 ug/L |
| Antioch, CA 2024 annual report | 62 ug/L |
| City of Antioch, CA 2024 annual report | 62 ug/L |
| City of Brentwood, CA 2024 annual report | 62 ug/L |
| City of Brentwood, CA 2024 annual report | 62 ug/L |
| City of Martinez, CA 2024 annual report | 62 ug/L |
| City of Martinez, CA 2024 annual report | 62 ug/L |
| City of Pittsburg, CA 2024 annual report | 62 ug/L |
| City of Pittsburg, CA 2024 annual report | 62 ug/L |
| Concord, CA 2024 annual report | 62 ug/L |
| Diablo Water District, CA 2024 annual report | 62 ug/L |
| Diablo Water District, CA 2024 annual report | 62 ug/L |
| Golden State Water Company, CA 2024 annual report | 62 ug/L |
| Golden State Water Company, CA 2024 annual report | 62 ug/L |
| Albany, NY 2024 annual report | 47.85–60.6 |
| Torrance, CA 2024 annual report | 14–60.1 ug/L |
| Avondale, AZ 2024 annual report | 4–60 ug/L |
| Fort Lauderdale, FL 2024 annual report | 17.3–59.9 ug/L |
| Jersey City, NJ 2024 annual report | 58.7 ug/L |
| Minneapolis, MN 2023 annual report | 10–58.3 |
| Mesquite, TX 2024 annual report | 58.2 ug/L |
| Fairfield, CA 2024 annual report | 58 ug/L |
| Washington Dc, DC 2023 annual report | 58 ug/L |
| Alameda, CA 2024 annual report | 57 ug/L |
| Albany, CA 2024 annual report | 57 ug/L |
| Berkeley, CA 2024 annual report | 57 ug/L |
| Castro Valley, CA 2024 annual report | 57 ug/L |
| Coral Springs, FL 2024 annual report | 27–57 ug/L |
| Crockett, CA 2024 annual report | 57 ug/L |
| El Cerrito, CA 2024 annual report | 57 ug/L |
| El Sobrante, CA 2024 annual report | 57 ug/L |
| Emeryville, CA 2024 annual report | 57 ug/L |
| Hayward, CA 2024 annual report | 57 ug/L |
| Hercules, CA 2024 annual report | 57 ug/L |
Showing 50 of 280. The full list is in the JSON API.
Frequently asked
+What is TTHM?
Total trihalomethanes — a group of four chemicals (including chloroform) formed when chlorine reacts with natural organic matter. Long-term exposure above the federal limit is linked to liver, kidney, and central-nervous-system effects and increased cancer risk.
+What is the federal limit for TTHM in drinking water?
The federal MCL for TTHM is 0.08 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 TTHM over the federal limit?
28 of the 395 public water systems on The Water Map report TTHM at or above its federal limit, spanning 45 U.S. states. The full list is on this page.
+How can I check if TTHM 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 TTHM.