PlainWater

National ranking · EPA SDWIS

Most Common Drinking Water Contaminants

Analytes ranked by total Safe Drinking Water Act violation records in EPA's SDWIS extract, a compliance ledger count, not a tap-water safety score.

50
Contaminants ranked
1,839,196
Most violations (one analyte)
98,293
Systems at #1 analyte

The verdict

Coliform (TCR) leads this extract with 1,839,196 recorded EPA violations across 98,293 public water systems; #50 on this list is Mercury at 49,728 violations.

1,839,196
Violations for Coliform (TCR)
49,728
#50 cutoff on this list
Top state for #1 analyte
30.1%
Health-based share at #1

Top 12 contaminants by violation volume

Longer bars = more recorded SDWIS violations nationwide

violations

What this shows Coliform (TCR) dominates the national violation ledger with 1,839,196 citations, roughly 553,598 health-based records in this extract.

Source EPA Safe Drinking Water Information System (SDWIS) As of 2026-05-15

Full ranking, top 50 contaminants

The Violations column's bar is proportional to Coliform (TCR)'s count, the highest in this list. Hover or focus a bar for its exact share of the leader and rank.

# Contaminant Violations Systems Health-based % Top state
1 Coliform (TCR) 1,839,196 100.0% of the leader · rank #1 · violations 98,293 30.1%
2 Revised Total Coliform Rule 710,085 38.6% of the leader · rank #2 · violations 60,574 9.2%
3 Nitrate 490,545 26.7% of the leader · rank #3 · violations 60,497 16.4%
4 TTHM 327,560 17.8% of the leader · rank #4 · violations 19,132 63.4%
5 Public Notice 326,526 17.8% of the leader · rank #5 · violations 32,526 0%
6 Lead and Copper Rule 316,481 17.2% of the leader · rank #6 · violations 41,280 8.2%
7 Total Haloacetic Acids (HAA5) 208,475 11.3% of the leader · rank #7 · violations 18,140 44%
8 Consumer Confidence Rule 201,666 11.0% of the leader · rank #8 · violations 29,061 0%
9 Chlorine 199,108 10.8% of the leader · rank #9 · violations 14,191 0.3%
10 Combined Uranium 184,297 10.0% of the leader · rank #10 · violations 4,427 10.2%
11 Arsenic 171,997 9.4% of the leader · rank #11 · violations 16,264 57.1%
12 Surface Water Treatment Rule 165,477 9.0% of the leader · rank #12 · violations 6,127 41.1%
13 Combined Radium (-226 and -228) 142,845 7.8% of the leader · rank #13 · violations 6,396 44.5%
14 Gross Alpha, Excl. Radon and U 137,468 7.5% of the leader · rank #14 · violations 14,784 24.1%
15 Radium-228 113,334 6.2% of the leader · rank #15 · violations 3,547 0%
16 Radium-226 108,989 5.9% of the leader · rank #16 · violations 3,237 0%
17 Groundwater Rule 103,689 5.6% of the leader · rank #17 · violations 7,907 53.1%
18 E. COLI 103,381 5.6% of the leader · rank #18 · violations 17,344 0%
19 Benzene 96,774 5.3% of the leader · rank #19 · violations 14,910 0.5%
20 Trichloroethylene 96,239 5.2% of the leader · rank #20 · violations 14,829 1.3%
21 Carbon tetrachloride 95,413 5.2% of the leader · rank #21 · violations 14,788 0.5%
22 1,1-Dichloroethylene 95,371 5.2% of the leader · rank #22 · violations 14,743 0.6%
23 1,1,1-Trichloroethane 94,855 5.2% of the leader · rank #23 · violations 14,739 0%
24 p-Dichlorobenzene 94,834 5.2% of the leader · rank #24 · violations 14,729 0%
25 1,2-Dichloroethane 94,715 5.1% of the leader · rank #25 · violations 14,710 0.1%
26 Tetrachloroethylene 94,265 5.1% of the leader · rank #26 · violations 14,507 1.4%
27 Toluene 92,883 5.1% of the leader · rank #27 · violations 14,460 0%
28 Ethylbenzene 92,796 5.0% of the leader · rank #28 · violations 14,446 0%
29 CHLOROBENZENE 92,339 5.0% of the leader · rank #29 · violations 14,392 0%
30 DICHLOROMETHANE 92,339 5.0% of the leader · rank #30 · violations 14,340 0.4%
31 Styrene 92,322 5.0% of the leader · rank #31 · violations 14,397 0%
32 cis-1,2-Dichloroethylene 92,275 5.0% of the leader · rank #32 · violations 14,401 0.1%
33 1,2-Dichloropropane 92,245 5.0% of the leader · rank #33 · violations 14,384 0.1%
34 trans-1,2-Dichloroethylene 92,022 5.0% of the leader · rank #34 · violations 14,358 0%
35 o-Dichlorobenzene 91,979 5.0% of the leader · rank #35 · violations 14,344 0%
36 1,1,2-Trichloroethane 91,189 5.0% of the leader · rank #36 · violations 14,235 0%
37 1,2,4-Trichlorobenzene 90,107 4.9% of the leader · rank #37 · violations 14,097 0%
38 Xylenes, Total 79,013 4.3% of the leader · rank #38 · violations 12,483 0%
39 Fluoride 78,347 4.3% of the leader · rank #39 · violations 13,411 36.1%
40 Vinyl chloride 76,766 4.2% of the leader · rank #40 · violations 12,475 0.3%
41 Nitrite 72,418 3.9% of the leader · rank #41 · violations 13,772 2.2%
42 Interim Enhanced Surface Water Treatment Rule 72,147 3.9% of the leader · rank #42 · violations 2,920 40%
43 Atrazine 52,999 2.9% of the leader · rank #43 · violations 9,462 2.3%
44 Selenium 52,594 2.9% of the leader · rank #44 · violations 13,645 6.3%
45 Nitrate-Nitrite 52,447 2.9% of the leader · rank #45 · violations 5,756 35.7%
46 Barium 50,993 2.8% of the leader · rank #46 · violations 13,488 3.2%
47 BHC-GAMMA 50,797 2.8% of the leader · rank #47 · violations 9,790 0%
48 Methoxychlor 50,526 2.7% of the leader · rank #48 · violations 9,743 0%
49 Cadmium 50,411 2.7% of the leader · rank #49 · violations 13,518 1.2%
50 Mercury 49,728 2.7% of the leader · rank #50 · violations 13,488 0.6%

Violation counts are cumulative SDWIS compliance records, not a live risk score for any single tap. Browse individual analyte profiles via the full contaminants directory.

Download the SDWIS/UCMR5 state landscape snapshot cited on this page: sdwis-state-landscape.csv (same CSV as /statistics, CC0).