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Water data study · Updated July 2026

Disinfection Byproducts (TTHM & HAA5) in U.S. Tap Water

Chlorine keeps tap water free of deadly germs — but it also reacts with natural matter to form “disinfection byproducts” linked to cancer risk over long exposure. We found 2,551 systems over the federal limit, serving about 20 million people.

20 million
people served by systems over the limit for disinfection byproducts
2,551 systems over the TTHM or HAA5 limit
Key findings
  • 2,551 public water systems reported TTHM or HAA5 above the EPA limit.
  • These byproducts form when chlorine disinfectant reacts with natural organic matter in the water.
  • It’s a genuine tradeoff: disinfection prevents deadly outbreaks; the byproducts carry a smaller long-term risk.
  • Carbon filters certified to NSF/ANSI 53 reduce TTHM — look for that specific certification.

What this means, in plain English

To kill germs that cause diseases like cholera, nearly all U.S. tap water is treated with chlorine. It works — waterborne outbreaks are rare. But chlorine also reacts with leaves, soil, and other natural material in the water to create tiny amounts of new chemicals called disinfection byproducts. The two the EPA regulates are TTHM and HAA5. Drinking high levels over many years is linked to a higher risk of bladder cancer, so there are federal limits. This isn’t a reason to stop disinfecting water — it’s a reason to filter the byproducts back out at your tap if your system runs high.

What you can do

If your system reports high TTHM or HAA5, a carbon filter certified to NSF/ANSI 53 (many under-sink and pitcher filters qualify) reduces them at the tap. Check your own system’s report for its latest levels.

Carbon filters certified to NSF/ANSI 53 reduce TTHM. Many under-sink and pitcher filters qualify — check for that specific certification.
See filters certified to reduce TTHM →

By state

States ranked by number of affected public water systems. Click a state for its city-by-city water quality.

# StateSystemsPeople served
1 Oklahoma 293 748,815
2 Texas 247 1,256,468
3 Florida 187 2,456,476
4 Louisiana 166 691,976
5 Kentucky 128 974,757
6 California 110 660,323
7 Arkansas 107 465,859
8 North Carolina 102 801,274
9 Missouri 91 210,383
10 Pennsylvania 89 932,581
11 West Virginia 87 213,806
12 Ohio 76 792,268
13 Illinois 75 169,264
14 Georgia 55 1,591,704
15 Puerto Rico 53 1,117,435
16 Alaska 53 43,753
17 Colorado 52 179,213
18 Washington 49 31,084
19 Mississippi 45 395,953
20 Virginia 42 215,384
21 South Carolina 35 502,208
22 Kansas 33 63,608
23 Alabama 30 626,061
24 Oregon 29 51,464
25 Arizona 28 776,099
26 New York 24 335,890
27 Maine 21 29,149
28 Tennessee 20 217,995
29 Montana 20 113,725
30 New Mexico 20 58,142
31 New Jersey 18 842,958
32 New Hampshire 17 55,893
33 Indiana 14 78,358
34 Idaho 12 17,842
35 Iowa 11 122,682
36 Michigan 11 13,739
37 Minnesota 11 12,198
38 Rhode Island 8 445,702
39 North Dakota 8 17,332
40 Wyoming 8 9,821
41 Connecticut 7 166,383
42 Nevada 5 20,871
43 Vermont 5 10,607
44 Utah 5 9,801
45 Wisconsin 4 40,795
46 South Dakota 4 20,356
47 Nebraska 3 37,685
48 Hawaii 1 1,000
49 American Samoa 1 402
50 Massachusetts 1 66

Most affected water systems

The 250 highest-ranking systems. Search for your city or utility.

# Water systemCityStateWorst DBP level
1 Fcsa 30 - El Porvenir Fresno CA 30937.5× limit
2 Pinellas Park Water Dept Pinellas Park FL 24886.2× limit
3 Vacation Village Condominiums Longwood FL 20396.3× limit
4 Montgomery Co Regional Pwa Mount Ida AR 11200.0× limit
5 Sunrise Springtree Sunrise FL 11121.1× limit
6 Nutrien-Suwannee River Chemical Complex White Springs FL 9130.0× limit
7 Sr-6 / I-75 Hamilton County Wtp Jasper FL 8125.0× limit
8 Suncoast Insulators Ocala FL 7503.3× limit
9 Everglades Holiday Park Oakland Park FL 7300.0× limit
10 Nutrien-Swift Creek Chemical Complex White Springs FL 5908.8× limit
11 Wildwood Mhp Ws West Monroe LA 5775.0× limit
12 East Columbia Water System Columbia LA 5700.0× limit
13 Costa Del Ray Miami FL 5666.7× limit
14 Atlantic Sugar Association Inc. Belle Glade FL 5482.4× limit
15 Maple Corner New York NY 5125.0× limit
16 Vixen Water System West Chatham LA 5016.7× limit
17 Hidden Oaks Subdivision Ws West Monroe LA 4975.0× limit
18 Cannon Creek Mhp Coral Gables FL 4887.5× limit
19 Dade Juvenile Residential Facility Tallahassee FL 4872.3× limit
20 Prairie Elem At New Raymer New Raymer CO 4816.7× limit
21 Hudson Gaars Mill Water System Dodson LA 4662.5× limit
22 Riverlandings Water Treatment Plant Naples FL 4541.7× limit
23 J ; S Fish Camp Cape Coral FL 4462.5× limit
24 Concord Water System Marion LA 4425.0× limit
25 Backwood Village Water System Saline LA 4287.5× limit
26 Union Parish Waterworks District 1 Farmerville LA 4212.5× limit
27 Canoe Creek Service Plaza Ft Lauderdale FL 4062.5× limit
28 Town Of Plain Dealing Water System Plain Dealing LA 3962.5× limit
29 Wards Chapel Water System Farmerville LA 3912.5× limit
30 Hwy 84 West Water Supply Winnfield LA 3900.0× limit
31 Mount Zion P S D Grantsville WV 3775.0× limit
32 Trail Ridge Landfill Jacksonville FL 3769.2× limit
33 Oak Park Okeechobee FL 3566.7× limit
34 Sandy Point 480 Water System Campti LA 3462.5× limit
35 East Central Bossier Water System Benton LA 3437.5× limit
36 Riviera Beach Utility District, City Of Riviera Beach FL 3425.0× limit
37 Red Gate Mobile Home Park Port Orchard WA 3376.7× limit
38 Belich Addition (Mahnomen) Cloquet MN 3366.7× limit
39 Point Wilhite Ws Downsville LA 3362.5× limit
40 Chesapeake Shores 3337.5× limit
41 Southwest Ouachita Waterworks, Inc West Monroe LA 3337.5× limit
42 Holmesville Water System Downsville LA 3262.5× limit
43 Village Of Chatham Water System Chatham LA 3250.0× limit
44 Fort Drum Service Plaza Ft Lauderdale FL 3175.8× limit
45 Tupper Lake V Tupper Lake NY 3116.7× limit
46 Vixen Water System Columbia LA 3050.0× limit
47 Bcwws 1A Pompano Beach FL 3044.6× limit
48 Fairview Union Water System Coushatta LA 3037.5× limit
49 Robeline Marthaville Water System Many LA 2950.0× limit
50 Sierra Country Club Coupeville WA 2866.2× limit
51 Mission Road Bellingham WA 2772.5× limit
52 Bentwood Subdivision Tavares FL 2735.3× limit
53 Hollis School Naukati Bay AK 2676.7× limit
54 Brenton Psd Brenton WV 2650.0× limit
55 Suwannee Valley Estates New Port Richey FL 2616.7× limit
56 Village Of Dubach Water System Dubach LA 2612.5× limit
57 Northgate Mobile Ranch Mims FL 2575.0× limit
58 Town Of Fort White Wtp Fort White FL 2527.5× limit
59 Union Springs Water System Converse LA 2512.5× limit
60 Darbonne Ws South Bernice LA 2475.0× limit
61 Golden State Water Company - South Shore Rancho Cordova CA 2458.3× limit
62 Wooten'S Mhp Longwood FL 2453.1× limit
63 Salem Water Board Salem WV 2450.0× limit
64 Eagle Lakes Wtp Orlando FL 2437.2× limit
65 Orient Water Company Republic WA 2421.7× limit
66 West Winn Water System Inc Winnfield LA 2412.5× limit
67 Town Of Ferriday Water System Ferriday LA 2387.5× limit
68 Woodglen Prd Water System Coupeville WA 2373.8× limit
69 New London Water Association Strong AR 2366.7× limit
70 Winebrook Hills Wd Newcomb NY 2366.7× limit
71 Havasu Wc Havasu Lake CA 2360.0× limit
72 Lakewood Park Subdivision Fort Pierce FL 2337.5× limit
73 River Grove Mobile Home Village Sebastian FL 2305.0× limit
74 Florida State Fire College Ocala FL 2300.0× limit
75 Sandy Ridge Labor Camp Naples FL 2276.7× limit
76 Port Buena Vista East Palatka FL 2260.8× limit
77 Micanopy Water System Micanopy FL 2260.2× limit
78 Tri-Water System Farmerville LA 2250.0× limit
79 Cedar Key Wtp Cedar Key FL 2238.9× limit
80 Magnolia Village Sarasota FL 2223.4× limit
81 Rpuma Crescent City FL 2215.6× limit
82 Brownville Water System West Monroe LA 2200.0× limit
83 Mexico Beach, City Of Mexico Beach FL 2183.3× limit
84 Township 29 Water Association Mt Vernon WA 2170.0× limit
85 Cypress Mhp Ramsey NJ 2162.5× limit
86 Lazy S Mobile Ranch Middletown CA 2158.3× limit
87 Oceana Community Of Oceana WV 2150.0× limit
88 Glen Rogers Psd Glen Rogers WV 2150.0× limit
89 Parker, City Of Water System Parker FL 2133.3× limit
90 Parry Trailer Village Boynton Bch FL 2127.8× limit
91 Myakka River St Pk Sarasota FL 2125.0× limit
92 Riverbend Estates Labelle FL 2113.0× limit
93 Cadeville Water District West Monroe LA 2100.0× limit
94 Beverly Beach Water System Longwood FL 2099.9× limit
95 Toscana Subdivision Ormond Beach FL 2091.7× limit
96 Harlem City Of Harlem MT 2087.5× limit
97 Village Of Castor Water System Castor LA 2066.7× limit
98 Devries Road Community Assn Coupeville WA 2056.7× limit
99 Hamrick Psd Hendricks WV 2050.0× limit
100 La Hispana #2 Cape Coral FL 2047.9× limit
101 Cleveland Pws Cleveland MO 2040.0× limit
102 Hidden Acres Estates Lorida FL 2035.0× limit
103 Olsons Greenhouse Fort Lupton CO 2028.8× limit
104 Madera Co Md1-Hidden Lake Estates Madera CA 2000.0× limit
105 Sunshine Learners Academy Inc. Orlando FL 1981.2× limit
106 Pendleton Water Association Many LA 1966.7× limit
107 Island Ptba Water System Coupeville WA 1947.5× limit
108 R.C. Willis Wtp (City Of Palatka) Palatka FL 1946.9× limit
109 Oak Creek Waterworks Oak Creek WI 1945.0× limit
110 Spring Point Homeowners Association Deer Harbor WA 1938.3× limit
111 Whidbey West Water Assoc. Coupeville WA 1937.5× limit
112 Coleman, City Of Coleman FL 1916.7× limit
113 Recycle America Of Orange Co. Orlando FL 1912.5× limit
114 Tamoshan Olympia WA 1895.0× limit
115 Marion Correctional Institution Ocala FL 1893.8× limit
116 Sumterville Water Treatment Plant Bushnell FL 1885.6× limit
117 Seminole Electric Combined-Cycle (Sccf) Palatka FL 1884.2× limit
118 Surfwood Mutual Water Corporation Mendocino CA 1883.3× limit
119 Tropical Breeze Estates, Inc Boynton Beach FL 1875.9× limit
120 Southwest Arkansas Water System Hope AR 1862.5× limit
121 Coffey Pws Coffey MO 1862.5× limit
122 Salt Creek Services, Inc. Bloomington IN 1855.0× limit
123 Fairway Number Three Water Friday Harbor WA 1835.0× limit
124 Salem Water Works Salem IN 1828.3× limit
125 Central Arkansas Water Paron Little Rock AR 1825.0× limit
126 Town Of Rayville Water System Rayville LA 1825.0× limit
127 Cotton Plant Water System Grayson LA 1812.5× limit
128 Cox Ferry Water System West Monroe LA 1812.5× limit
129 City Of Dos Palos Dos Palos CA 1787.5× limit
130 Holiday Travel Park Bunnell FL 1771.9× limit
131 Big Cypress Park Headquarters Ochopee FL 1753.8× limit
132 Swfrec Tallahassee FL 1751.1× limit
133 Elizabeth Water Dept Elizabeth WV 1750.0× limit
134 Charles Town Utilities Charles Town WV 1750.0× limit
135 Maysville Pws Maysville MO 1750.0× limit
136 Novaphos Developement Llc Fort Meade FL 1743.8× limit
137 Paradise Park Condo. Assoc. Punta Gorda FL 1737.7× limit
138 Faith Farm Ministries Boynton Beach FL 1734.9× limit
139 Penn Cove Water And Sewer District Oak Harbor WA 1734.4× limit
140 Lake Manor Mhp Stuart FL 1727.5× limit
141 Lackamas Elementary School Port Orchard WA 1718.3× limit
142 Murphy Elma Veneer Port Orchard WA 1716.2× limit
143 Oasis Church Ormond Beach FL 1700.0× limit
144 Oysterville Water Oysterville WA 1700.0× limit
145 Colonial Estates Mhp Boynton Beach FL 1698.1× limit
146 Buttonwood Bay Mhp Southfield MI 1683.6× limit
147 Camano Sunset Water System Mount Vernon WA 1677.2× limit
148 Palm Lake Estates North Riviera Beach FL 1676.0× limit
149 Culbertson Water System Choudrant LA 1662.5× limit
150 Northwest Florida Reception Center Tallahassee FL 1658.9× limit
151 Briarwood Water System Freeland WA 1655.0× limit
152 Walnut Hill Water Association Bradley AR 1650.0× limit
153 Gunnery Road Baptist Church And School Lehigh Acres FL 1640.0× limit
154 Tri County Rwdd -Moores Chapel Russellville AR 1637.5× limit
155 North Lake St John Water System Gilbert LA 1637.5× limit
156 Wakulla Regional (Aka Gulf Coast) Quincy FL 1635.3× limit
157 Redlands Christian Migrant Association Immokalee FL 1625.0× limit
158 Village Of Hosston Water System Hosston LA 1625.0× limit
159 Hico Water System Dubach LA 1625.0× limit
160 Mullett Lake Water Association Geneva FL 1616.7× limit
161 Catskill Village Catskill NY 1606.7× limit
162 The Nest School Lutz FL 1606.2× limit
163 Peniel Baptist Church ; Academy Palatka FL 1603.2× limit
164 Lee Cypress Co-Op New Port Richey FL 1591.7× limit
165 Miami Pws Miami MO 1587.5× limit
166 Monroe City Pws Monroe MO 1587.5× limit
167 Trees Camp Wtp Lehigh Acres FL 1586.9× limit
168 Magnolia-Spring Creek Subdivision Des Peres MO 1583.3× limit
169 Rainelle Water Dept Rainelle WV 1583.3× limit
170 Blackwater Pws Blackwater MO 1575.0× limit
171 Sheridan Pws Sheridan MO 1575.0× limit
172 Yankeetown Wtp Yankeetown FL 1572.0× limit
173 Mountain Ridge Roslyn WA 1570.1× limit
174 Arrowhead Beach Coop Water Assoc Mt Vernon WA 1570.0× limit
175 Southern Truss Ft. Pierce FL 1568.8× limit
176 Mount Ida Waterworks Mount Ida AR 1566.7× limit
177 Hannah Heights #2 Water Users Assn Friday Harbor WA 1558.4× limit
178 Indian River Shores Mhp Micco FL 1555.6× limit
179 Shelter Cove Resort St Cloud FL 1550.2× limit
180 Paw Paw Route 19 Psd Westover WV 1550.0× limit
181 Hammock Pointe Utility Association Inc Kissimmee FL 1550.0× limit
182 Riverview Colony Chester MT 1550.0× limit
183 Cal Fire Baseline Conservation Camp Jamestown CA 1550.0× limit
184 Blodgett Pws Blodgett MO 1548.3× limit
185 Florida Grande Motor Coach Resort Greenwood Village CO 1547.6× limit
186 Colorado City Md Colorado City CO 1534.2× limit
187 Huttig Waterworks Huttig AR 1525.0× limit
188 Emporia, City Of Emporia VA 1516.7× limit
189 Beverly Beach Improvement Club Mt Vernon WA 1510.6× limit
190 Palm Circle Cottages And Mhp Stuart FL 1510.6× limit
191 Rolling Hills-Glencairn Oak Harbor WA 1508.8× limit
192 Nelson Pws Nelson MO 1500.0× limit
193 North Vernon Water Department North Vernon IN 1498.3× limit
194 Lauderhill, City Of Lauderhill FL 1495.8× limit
195 Westgate River Ranch ; Rv Resort Orlando FL 1491.9× limit
196 Stucker Fork Water Utility Austin IN 1491.7× limit
197 Longmire Ashford WA 1490.0× limit
198 Clover Psd Spencer WV 1488.3× limit
199 Jenkins Community Water System Doyline LA 1487.5× limit
200 Lamar Pws Lamar MO 1487.5× limit
201 Town Of Olla Water System Olla LA 1487.5× limit
202 Wvdhhr Mullens WV 1483.3× limit
203 East Toho Fka Boggy Creek Resort Kissimmee FL 1480.9× limit
204 Usfs Pinecrest Rec Area Sonora CA 1475.0× limit
205 Lake Chicot Water Supply Association Lake Village AR 1475.0× limit
206 St Labre Indian School Ashland MT 1472.5× limit
207 Cape San Juan Water District Friday Harbor WA 1470.0× limit
208 Dundee, Town Of Dundee FL 1470.0× limit
209 West Palm Beach Wtp West Palm Beach FL 1465.3× limit
210 Rcma Labelle Cdc Immokalee FL 1459.4× limit
211 Springfield, City Of Springfield FL 1454.6× limit
212 Chicot Junction Water Assoc Lake Village AR 1450.0× limit
213 Havana Waterworks Havana AR 1450.0× limit
214 Brown County State Park Nashville IN 1446.7× limit
215 Lalumina Llc. Sorrento LA 1437.5× limit
216 Deepwoods Utilities Inc Keithville LA 1437.5× limit
217 City Of Perry Perry FL 1434.2× limit
218 Sunrise Community Miami FL 1434.1× limit
219 Delanson Village Water Works Delanson NY 1434.1× limit
220 Tiber County Water District Brady MT 1433.3× limit
221 Gulf County Water Department Port St. Joe FL 1430.0× limit
222 Hope Forest Academy Minden NV 1427.9× limit
223 Cooper County Consolidated Pwsd # 1 Boonville MO 1425.0× limit
224 Louisiana Pws Louisiana MO 1425.0× limit
225 West Milford Water Works West Milford WV 1425.0× limit
226 Country Walk Utilities, Inc. New Port Richey FL 1415.7× limit
227 St. Helena, City Of St. Helena CA 1414.5× limit
228 Waverly Pws Waverly MO 1412.5× limit
229 South Monroe Ws Gowc West Monroe LA 1412.5× limit
230 Holum Water System Grayson LA 1412.5× limit
231 New Franklin Pws New Franklin MO 1412.5× limit
232 Seawest Water System Mt Vernon WA 1407.5× limit
233 Mcdowell County Psd Premier 1400.0× limit
234 Sweet Springs Pws Sweet Springs MO 1400.0× limit
235 Pleasant Ridge Water System Olla LA 1400.0× limit
236 Charmingdale Subdivision Ws West Monroe LA 1400.0× limit
237 Village Of Eros Water System Eros LA 1400.0× limit
238 Pinesdale Town Of Pinesdale MT 1400.0× limit
239 Bodcaw Rural Water System Rosston AR 1400.0× limit
240 Montrose Boydell Water System Montrose AR 1400.0× limit
241 High Springs Wtp High Springs FL 1399.0× limit
242 Kissimmee River Park And Marina Lake Wales FL 1398.3× limit
243 Tropical Research ; Education Center Tallahassee FL 1393.4× limit
244 Ne Yell County Water Assoc Dardanelle AR 1387.5× limit
245 Mill Creek Wia Dumont CO 1387.5× limit
246 Panoramic Mesa Subd Silt CO 1387.2× limit
247 Vc/Cassadaga Water Supply (Ws#5) Deland FL 1383.3× limit
248 Ministers Run Water Assoc Rivesville WV 1383.3× limit
249 East Putnam Regional East Palatka FL 1379.9× limit
250 E.L.C. Water System Eastsound WA 1376.2× limit

Terms, explained

Disinfection byproducts
New chemicals that form when a disinfectant like chlorine reacts with natural material in water. Small amounts are an unavoidable side effect of keeping water germ-free.
TTHM (total trihalomethanes)
A group of four disinfection byproducts the EPA limits to 80 parts per billion. Chloroform is the most common one.
HAA5 (haloacetic acids)
A group of five disinfection byproducts the EPA limits to 60 parts per billion.
Why chlorine at all?
Chlorine disinfection is one of the biggest public-health wins in history, ending widespread deadly waterborne disease. Byproducts are the manageable price of that protection.

Methodology & sources

EPA SDWIS and compliance monitoring data. Federal limits: 80 ppb for TTHM and 60 ppb for HAA5 (running annual averages).

Important caveat: Byproduct levels swing seasonally (higher in warm months) and by location in the distribution system, so a single reading is a snapshot, not a constant.

This study draws on 21,807 U.S. public water systems and our full certified-filter database. All EPA data is public domain.

For journalists & researchers

Every figure on this page is free to republish with attribution and a link — no permission needed (CC-BY 4.0).

Cite this study

VerifiedWaterFilterData (July 2026). "Disinfection Byproducts (TTHM & HAA5) in U.S. Tap Water." Analysis of EPA public drinking-water and NSF/WQA/IAPMO certification data. https://verifiedwaterfilterdata.com/studies/disinfection-byproducts-in-tap-water/

Download the data (JSON) Full methodology

Need a custom cut — a single state, county, or contaminant? The underlying data supports it; get in touch.

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