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U.S. Drinking Water Quality

Health violation data for 49,190 community water systems across all 50 states. Based on EPA Safe Drinking Water Information System (SDWIS) data.

Water Systems
49,190
Population Served
328,216,824
Systems with Health Violations
18,118
Total Health Violations
314,259

State Water Quality Rankings

Ranked by percentage of community water systems with health-based violations. Lower is better.

# State Systems With Violations % Affected
1 Oklahoma 883 812 92%
2 Puerto Rico 402 324 80.6%
3 U.S. Virgin Islands 18 14 77.8%
4 District of Columbia 12 9 75%
5 New Mexico 590 440 74.6%
6 American Samoa 10 7 70%
7 Vermont 380 264 69.5%
8 Alaska 404 274 67.8%
9 Louisiana 835 550 65.9%
10 West Virginia 424 268 63.2%
11 Nebraska 596 352 59.1%
12 Arkansas 667 380 57%
13 Kentucky 376 195 51.9%
14 South Dakota 512 260 50.8%
15 Utah 559 275 49.2%
16 Connecticut 503 236 46.9%
17 Rhode Island 92 42 45.7%
18 Arizona 956 435 45.5%
19 Nevada 228 103 45.2%
20 Wisconsin 977 432 44.2%
21 Kansas 858 372 43.4%
22 Pennsylvania 1,787 772 43.2%
23 New Hampshire 678 284 41.9%
24 Massachusetts 564 236 41.8%
25 Oregon 938 390 41.6%
26 California 3,077 1,274 41.4%
27 Idaho 767 311 40.5%
28 Texas 4,587 1,807 39.4%
29 Maryland 456 179 39.3%
30 Wyoming 316 123 38.9%
31 Colorado 1,109 429 38.7%
32 New York 2,201 803 36.5%
33 Northern Mariana Islands 36 13 36.1%
34 Illinois 1,783 642 36%
35 Indiana 718 254 35.4%
36 Missouri 1,666 562 33.7%
37 North Carolina 1,965 656 33.4%
38 New Jersey 619 206 33.3%
39 Mississippi 990 316 31.9%
40 Maine 361 114 31.6%
41 South Carolina 557 161 28.9%
42 Tennessee 453 129 28.5%
43 Ohio 1,094 310 28.3%
44 Florida 1,516 410 27%
45 Montana 809 198 24.5%
46 Delaware 209 50 23.9%
47 Virginia 1,054 235 22.3%
48 Michigan 1,433 314 21.9%
49 North Dakota 318 55 17.3%
50 Alabama 543 91 16.8%
51 Hawaii 118 16 13.6%
52 Washington 2,397 295 12.3%
53 Georgia 1,715 201 11.7%
54 Minnesota 993 115 11.6%
55 Iowa 1,077 121 11.2%

Most Common Contaminants

Health-based violations by contaminant type across all U.S. water systems.

Contaminant Violations Systems Affected
Total Trihalomethanes (TTHM) 53,036 2,715
Haloacetic Acids (HAA5) 21,348 1,585
Barium 19,993 779
Fluoride 14,728 3,142
Nitrate 8,701 610
Lead & Copper Rule 8,150 395
Arsenic 6,671 1,155
Combined Radium 226/228 6,345 2,938
Turbidity 6,319 703
Copper 5,767 305
Total Coliform (RTCR) 5,765 1,942
E. coli 5,491 2,276
Gross Alpha 5,201 4,950
Manganese 5,169 133
Lead (Action Level) 4,571 188

Explore More

All Contaminants → Air Quality Rankings → All States → Superfund Sites → Toxic Chemicals →

About This Data

Water quality data is from the EPA Safe Drinking Water Information System (SDWIS). Health-based violations include Maximum Contaminant Level (MCL) and Treatment Technique (TT) violations that may pose a risk to public health. Monitoring and reporting violations are not included in health-based counts.

Source: U.S. Environmental Protection Agency, SDWIS Federal Reporting Services U.S. Environmental Protection Agency, SDWIS Federal Reporting Services