Disinfection byproducts
TTHM in U.S. tap water
1,124 public water systems across 44 U.S. states report TTHM in their annual Consumer Confidence Report. 46 sit at or above the federal limit.
1124
systems measuring
46
over the limit
44
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 limit80 ug/L· MCL
At or above the federal limit (46)
| Water system | Measured | vs. limit |
|---|---|---|
| Alco Water Service — Salinas, Ca, CA 2023 annual report | 0.63 mg/L | 7.9× the limit |
| Jackson, MS 2024 annual report | 17.7–131 ug/L | 1.6× the limit |
| Page Avenue Mutual Water Company — Fullerton, Ca, CA 2020 annual report | 0.12 mg/L | 1.5× 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 |
| Hollywood, FL 2024 annual report | 6.6–111.6 ug/L | 1.4× the limit |
| High Point, NC 2024 annual report | 111 ug/L | 1.4× the limit |
| California Rehabilitation Center - Norco — Norco, Ca, CA 2022 annual report | 8.8–110 ug/L | 1.4× the limit |
| Pismo Beach Water Department — Pismo Beach, Ca, CA 2023 annual report | 34–110 ug/L | 1.4× the limit |
| San Angelo, TX 2024 annual report | 66.9–110 ug/L | 1.4× the limit |
| Goodyear, AZ 2024 annual report | 104 ug/L | 1.3× the limit |
| Laredo, TX 2024 annual report | 32.5–103 ug/L | 1.3× the limit |
| El Paso, TX 2024 annual report | 0–100 ug/L | 1.3× the limit |
| Akron, OH 2024 annual report | 32.4–98.3 ug/L | 1.2× the limit |
| Quartz Hill Water Dist. — Quartz Hill, Ca, CA 2022 annual report | 18–97.1 ug/L | 1.2× the limit |
| Midland, TX 2024 annual report | 0–97 ug/L | 1.2× the limit |
| Odessa, TX 2024 annual report | 2.53–96.4 ug/L | 1.2× the limit |
| Atlanta, GA 2024 annual report | 14.4–95.8 ug/L | 1.2× the limit |
| Arrowhead Villas Mutual Service Company — Skyforest, Ca, CA 2023 annual report | 16–93.7 ug/L | 1.2× the limit |
| San Dieguito Wd — Encinitas, Ca, CA 2023 annual report | 11–93 ug/L | 1.2× the limit |
| Suisun-solano Water Authority — Vacaville, Ca, CA 2023 annual report | 93 ug/L | 1.2× the limit |
| Brunswick, MD 2024 annual report | 24.62–92.76 ug/L | 1.2× the limit |
| Avenal, City of — Avenal, Ca, CA 2023 annual report | 38–92 ug/L | 1.1× the limit |
| Nacimiento Water Company — Bradley, Ca, CA 2023 annual report | 26–92 ug/L | 1.1× the limit |
| Jacksonville, FL 2024 annual report | 25.71–91.49 ug/L | 1.1× the limit |
| Baltimore, MD 2023 annual report | 23.6–91.2 ug/L | 1.1× the limit |
| Metropolitan of Baltimore, MD 2024 annual report | 23.6–91.2 ug/L | 1.1× the limit |
| Billings, MT 2024 annual report | 17–91 ug/L | 1.1× the limit |
| New Braunfels, TX 2024 annual report | 0–90.9 ug/L | 1.1× the limit |
| West Palm Beach, FL 2024 annual report | 13.9–90.1 ug/L | 1.1× the limit |
| Firebaugh City — Firebaugh, Ca, CA 2023 annual report | 22–86 ug/L | 1.1× the limit |
| Sweetwater Authority — Chula Vista, Ca, CA 2023 annual report | 4.6–85.46 ug/L | 1.1× the limit |
| Keswick Multi Care Center, MD 2024 annual report | 50–85.4 ug/L | 1.1× the limit |
| Santa Fe I.d. — Rancho Santa Fe, Ca, CA 2023 annual report | 11–85 ug/L | 1.1× the limit |
| Shreveport, LA 2024 annual report | 12–85 ug/L | 1.1× the limit |
| Crestline Village Cwd - Division 10 — Crestline, Ca, CA 2023 annual report | 18.5–84.3 ug/L | 1.1× the limit |
| Columbus, OH 2025 annual report | 16.5–83.9 ug/L | 1.0× the limit |
| Athens, GA 2024 annual report | 0–83.6 ug/L | 1.0× the limit |
| Mendota, City of — Mendota, Ca, CA 2023 annual report | 28–82 ug/L | 1.0× the limit |
| Shasta C.s.d. — Shasta, Ca, CA 2023 annual report | 35–82 ug/L | 1.0× the limit |
| Westmorland, City of — Westmorland, Ca, CA 2022 annual report | 82 ug/L | 1.0× the limit |
| Beverly Hills-city, Water Dept. — Beverly Hills, Ca, CA 2021 annual report | 6–80 ug/L | 1.0× the limit |
| Calistoga, City of — Calistoga, Ca, CA 2021 annual report | 30–80 ug/L | 1.0× the limit |
| City of West Sacramento — West Sacramento, Ca, CA 2022 annual report | 80 ug/L | 1.0× the limit |
| Frisco, TX 2024 annual report | 80 ug/L | 1.0× the limit |
| Sacramento Suburban Water District — Sacramento, Ca, CA 2023 annual report | 41–80 ug/L | 1.0× the limit |
Approaching the limit (96)
| Water system | Measured | vs. limit |
|---|---|---|
| Quartz Hill Water Dist. — Quartz Hill, Ca, CA 2023 annual report | 29.2–79.7 ug/L | 1.0× the limit |
| Cdcr California Health Care Facility — Stockton, Ca, CA 2023 annual report | 11–79 ug/L | 1.0× the limit |
| Valencia Heights Water Co. — West Covina, Ca, CA 2021 annual report | 19–79 ug/L | 1.0× the limit |
| Yuma, AZ 2025 annual report | 79 ug/L | 1.0× the limit |
| Beverly Hills-city, Water Dept. — Beverly Hills, Ca, CA 2022 annual report | 11–78 ug/L | 1.0× the limit |
| City of Pleasanton — Pleasanton, Ca, CA 2023 annual report | 78 ug/L | 1.0× the limit |
| Springfield, MA 2024 annual report | 49–78 ug/L | 1.0× the limit |
| Las Vegas, NV 2023 annual report | 77 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 |
| Quartz Hill Water Dist. — Quartz Hill, Ca, CA 2020 annual report | 0–76.7 ug/L | 1.0× the limit |
| Quartz Hill Water Dist. — Quartz Hill, Ca, CA 2021 annual report | 0–76.7 ug/L | 1.0× the limit |
| Nevada Id - Lake Wildwood — Grass Valley, Ca, CA 2020 annual report | 35–76.6 ug/L | 1.0× the limit |
| Nevada Id - North Auburn — Grass Valley, Ca, CA 2021 annual report | 18–76.5 ug/L | 1.0× the limit |
| Avila Beach Community Services District — Avila Beach, Ca, CA 2023 annual report | 22–76 ug/L | 0.9× the limit |
| City of Buellton Water Division — Buellton, Ca, CA 2023 annual report | 22–76 ug/L | 0.9× the limit |
| Morro Bay Pw Dept - Water Division — Morro Bay, Ca, CA 2023 annual report | 22–76 ug/L | 0.9× the limit |
| Santa Ynez River Water Cons. Dist. Id#1 — Santa Ynez, Ca, CA 2023 annual report | 22–76 ug/L | 0.9× the limit |
| Solvang Water Division — Solvang, Ca, CA 2023 annual report | 22–76 ug/L | 0.9× the limit |
| Armona Community Services Dist — Armona, Ca, CA 2023 annual report | 74–75 ug/L | 0.9× the limit |
| Oceano Comm Services Dist. — Oceano, Ca, CA 2021 annual report | 13–75 ug/L | 0.9× the limit |
| San Luis Obispo Water Department — San Luis Obispo, Ca, CA 2023 annual report | 27–75 ug/L | 0.9× the limit |
| Aurora, IL 2024 annual report | 31.3–74.9 ug/L | 0.9× the limit |
| El Segundo-city, Water Dept. — El Segundo, Ca, CA 2022 annual report | 16–74 ug/L | 0.9× the limit |
| Heritage Ranch Csd — Paso Robles, Ca, CA 2023 annual report | 18–74 ug/L | 0.9× the limit |
| So. Cal. Edison Co.-santa Catalina — Avalon, Ca, CA 2021 annual report | 74 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 |
| Calif State Polytechnical Univ - Pomona — Pomona, Ca, CA 2022 annual report | 73.75 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 |
| Calexico, City of — Calexico, Ca, CA 2023 annual report | 73 ug/L | 0.9× the limit |
| City of Benicia — Benicia, Ca, CA 2023 annual report | 73 ug/L | 0.9× the limit |
| North Marin Water District — Novato, Ca, CA 2023 annual report | 0–73 ug/L | 0.9× the limit |
| City of Paso Robles Water Division — Paso Robles, Ca, CA 2023 annual report | 9.3–72.8 ug/L | 0.9× the limit |
| Vista Irrigation District — Vista, Ca, CA 2023 annual report | 15.2–72.5 ug/L | 0.9× the limit |
| Crescenta Valley Cwd — La Crescenta, Ca, CA 2022 annual report | 27.4–72.2 ug/L | 0.9× the limit |
| Camp Pendleton (north) — Camp Pendleton, Ca, CA 2023 annual report | 5.9–72 ug/L | 0.9× the limit |
| Camp Pendleton (south) — Camp Pendleton, Ca, CA 2023 annual report | 5.9–72 ug/L | 0.9× the limit |
| Edmond, OK 2024 annual report | 72 ug/L | 0.9× the limit |
| Los Angeles Cwwd 40 Reg 4 & 34 Lancaster — Alhambra, Ca, CA 2023 annual report | 72 ug/L | 0.9× the limit |
| Santa Cruz Water Department — Santa Cruz, Ca, CA 2023 annual report | 9–72 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 | 11–71 ug/L | 0.9× the limit |
| City of North Miami Beach, FL 2023 annual report | 11–71 ug/L | 0.9× the limit |
| Miami Dade, FL 2023 annual report | 11–71 ug/L | 0.9× the limit |
| Grand Rapids, MI 2025 annual report | 70.7 ug/L | 0.9× the limit |
| Buffalo, NY 2023 annual report | 15.2–70.2 ug/L | 0.9× the limit |
| Blythe - City of — Blythe, Ca, CA 2022 annual report | 70 ug/L | 0.9× the limit |
| City of Hemet, CA 2024 annual report | 2.7–70 ug/L | 0.9× the limit |
| City of Menifee, CA 2024 annual report | 9.1–70 ug/L | 0.9× the limit |
| City of Murrieta, CA 2024 annual report | 2.7–70 ug/L | 0.9× the limit |
| City of San Jacinto, CA 2024 annual report | 2.7–70 ug/L | 0.9× the limit |
| East Valley Service Area, CA 2024 annual report | 2.7–70 ug/L | 0.9× the limit |
| Mills Service Area, CA 2024 annual report | 2.7–70 ug/L | 0.9× the limit |
| Moreno Valley, CA 2024 annual report | 2.7–70 ug/L | 0.9× the limit |
| Calif State Polytechnical Univ - Pomona — Pomona, Ca, CA 2023 annual report | 69.25 ug/L | 0.9× the limit |
| Mcallen, TX 2024 annual report | 18.5–69.2 ug/L | 0.9× the limit |
| Purissima Hills Water District — Los Altos Hills, Ca, CA 2022 annual report | 69.1 ug/L | 0.9× the limit |
| Topeka, KS 2024 annual report | 32.6–69.1 ug/L | 0.9× the limit |
| Crescenta Valley Cwd — La Crescenta, Ca, CA 2021 annual report | 26–69 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 | 0.9× the limit |
| Phoenix, AZ 2025 annual report | 4–68 ug/L | 0.9× the limit |
| Macon, GA 2023 annual report | 21.6–67.9 ug/L | 0.8× the limit |
| California Water Service Co-leona Valley — San Jose, Ca, CA 2023 annual report | 67.8 ug/L | 0.8× the limit |
| Columbia, SC 2024 annual report | 15–67 ug/L | 0.8× the limit |
| Placer Cwa - Auburn/bowman — Auburn, Ca, CA 2022 annual report | 27–67 ug/L | 0.8× the limit |
| Suffolk, VA 2024 annual report | 67 ug/L | 0.8× the limit |
| Western Hills Water District/diablo Gran — Patterson, Ca, CA 2023 annual report | 9.1–67 ug/L | 0.8× the limit |
| Camarillo Water Dept — Camarillo, Ca, CA 2023 annual report | 1.9–66 ug/L | 0.8× the limit |
| Heber Public Utility District — Heber, Ca, CA 2023 annual report | 66 ug/L | 0.8× the limit |
| Henderson, NV 2024 annual report | 66 ug/L | 0.8× the limit |
| Pasadena, CA 2023 annual report | 6–66 ug/L | 0.8× the limit |
| Tesoro Viejo Master Mwc, Inc. — San Jose, Ca, CA 2023 annual report | 66 ug/L | 0.8× the limit |
| Lake Arrowhead Csd — Lake Arrowhead, Ca, CA 2023 annual report | 65.9 ug/L | 0.8× the limit |
| Chandler, AZ 2024 annual report | 65 ug/L | 0.8× the limit |
| Foothill Municipal Water Dist. — La Canada Flintridge, Ca, CA 2022 annual report | 13–65 ug/L | 0.8× the limit |
| Vallecitos Wd — San Marcos, Ca, CA 2023 annual report | 4.2–65 ug/L | 0.8× the limit |
| St. Helena, City of — St. Helena, Ca, CA 2023 annual report | 64.76 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 |
| Broken Arrow, OK 2024 annual report | 64 ug/L | 0.8× the limit |
| California Water Service Co.-lancaster — San Jose, Ca, CA 2023 annual report | 64 ug/L | 0.8× the limit |
| California Water Service Co.-travis Afb — San Jose, Ca, CA 2023 annual report | 64 ug/L | 0.8× the limit |
| Charlotte, NC 2024 annual report | 64 ug/L | 0.8× the limit |
| Cws - Bakersfield — San Jose, Ca, CA 2023 annual report | 64 ug/L | 0.8× the limit |
| Manhattan Beach-city, Water Dept. — Manhattan Beach, Ca, CA 2021 annual report | 64 ug/L | 0.8× the limit |
| Stamford, CT 2024 annual report | 64 ug/L | 0.8× the limit |
Within the federal limit (982)
Showing 50 of 982. 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 80 ug/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?
46 of the 1124 public water systems on The Water Map report TTHM at or above its federal limit, spanning 44 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.