Contaminant guide

What's measured in US tap water

Every contaminant US water suppliers report to the EPA — what it is, the legal limit, and how often it actually turns up. Pick one to see where.

All contaminants

Sorted by how many water suppliers detected each one. “Over limit” is only counted where the published figure is the one the limit is written against — the lead and copper 90th percentile.

ContaminantEPA limitDetected in Over limitSource
Lead 0.0150 mg/L 47,629 measured 4,246 LCR
Copper 1300 µg/L 32,617 (89%) SYR4
TTHM 80 µg/L 30,898 (86.9%) SYR4
Lead 15 µg/L 28,796 (79.8%) SYR4
Total Haloacetic Acids (HAA5) 60 µg/L 27,470 (80.7%) SYR4
Barium 2000 µg/L 26,603 (78.9%) SYR4
Fluoride 4000 µg/L 25,909 (76.5%) SYR4
Nitrate 10000 µg/L 24,520 (82.6%) SYR4
Chloroform 24,215 (71.6%) SYR4
Bromodichloromethane 24,091 (71.4%) SYR4
Dibromochloromethane 23,644 (70.1%) SYR4
Dichloroacetic Acid 19,963 (69.6%) SYR4
Nitrate-Nitrite 10000 µg/L 18,509 (76.7%) SYR4
Trichloroacetic Acid 17,340 (60.4%) SYR4
Dibromoacetic Acid 16,842 (58.7%) SYR4
Bromoform 16,756 (49.7%) SYR4
Arsenic 10 µg/L 15,303 (45%) SYR4
Combined Radium (-226 And -228) 5 pCi/L 14,619 (69.7%) SYR4
Chromium 100 µg/L 10,760 (31.9%) SYR4
Monochloroacetic Acid 10,754 (37.5%) SYR4
Gross Alpha, Excl. Radon And U 15 pCi/L 9,273 (57.2%) SYR4
Monobromoacetic Acid 8,205 (28.6%) SYR4
Selenium 50 µg/L 7,995 (23.7%) SYR4
Combined Uranium 30 µg/L 7,746 (44.1%) SYR4
Gross Beta Particle Activity 6,294 (58.8%) SYR4
Lithium 3,552 (36.7%) UCMR-5
Xylenes, Total 10000 µg/L 3,013 (9.7%) SYR4
Di(2-ethylhexyl) Phthalate 6 µg/L 2,772 (11.1%) SYR4
Nitrite 1000 µg/L 2,483 (10.2%) SYR4
Cyanide 200 µg/L 2,240 (8.7%) SYR4
Antimony, Total 6 µg/L 2,090 (6.2%) SYR4
Pfpea 1,948 (20.1%) UCMR-5
Pfba 1,819 (18.8%) UCMR-5
Pfhxa 1,707 (17.6%) UCMR-5
PFBS 1,599 (16.5%) UCMR-5
Toluene 1000 µg/L 1,467 (4.2%) SYR4
Thallium, Total 2 µg/L 1,396 (4.1%) SYR4
Atrazine 3 µg/L 1,368 (4.6%) SYR4
Ethylbenzene 700 µg/L 1,362 (3.9%) SYR4
PFOS 1,290 (13.3%) UCMR-5
PFOA 1,222 (12.6%) UCMR-5
Mercury 2 µg/L 1,160 (3.4%) SYR4
Cadmium 5 µg/L 1,044 (3.1%) SYR4
PFHXS 970 (10%) UCMR-5
Dalapon 200 µg/L 840 (3.1%) SYR4
Tetrachloroethylene 5 µg/L 768 (2.2%) SYR4
Beryllium, Total 4 µg/L 658 (2%) SYR4
Dichloromethane 5 µg/L 602 (1.7%) SYR4
Trichloroethylene 5 µg/L 567 (1.6%) SYR4
Pfhpa 529 (5.5%) UCMR-5
Simazine 4 µg/L 477 (1.7%) SYR4
Carbon Tetrachloride 5 µg/L 438 (1.3%) SYR4
Chlorite 1000 µg/L 356 (78.1%) SYR4
2,4-D 70 µg/L 309 (1.1%) SYR4
Hexachlorocyclopentadiene 50 µg/L 288 (1.1%) SYR4
cis-1,2-Dichloroethylene 70 µg/L 286 (0.8%) SYR4
Di(2-ethylhexyl) Adipate 400 µg/L 227 (0.9%) SYR4
Styrene 100 µg/L 226 (0.7%) SYR4
1,1-Dichloroethylene 7 µg/L 224 (0.6%) SYR4
1,2-DIBROMO-3-CHLOROPROPANE 0.2000 µg/L 223 (0.9%) SYR4
P-Dichlorobenzene 75 µg/L 199 (0.6%) SYR4
Picloram 500 µg/L 187 (0.7%) SYR4
Asbestos 7 MFL 186 (1.8%) SYR4
Pentachlorophenol 1 µg/L 186 (0.7%) SYR4
Benzo(A)Pyrene 0.2000 µg/L 184 (0.7%) SYR4
6:2 Fts 179 (1.8%) UCMR-5
Benzene 5 µg/L 174 (0.5%) SYR4
Bromate 10 µg/L 167 (49.4%) SYR4
1,2-Dichloroethane 5 µg/L 166 (0.5%) SYR4
1,1,1-Trichloroethane 200 µg/L 160 (0.5%) SYR4
Heptachlor Epoxide 0.2000 µg/L 159 (0.6%) SYR4
Ethylene Dibromide 0.0500 µg/L 137 (0.5%) SYR4
Hexachlorobenzene 1 µg/L 125 (0.5%) SYR4
Chlorobenzene 100 µg/L 117 (0.3%) SYR4
1,2-Dichloropropane 5 µg/L 107 (0.3%) SYR4
Vinyl Chloride 2 µg/L 105 (0.3%) SYR4
Chlordane 2 µg/L 99 (0.4%) SYR4
trans-1,2-Dichloroethylene 100 µg/L 99 (0.3%) SYR4
Diquat 20 µg/L 96 (0.7%) SYR4
Endrin 2 µg/L 96 (0.4%) SYR4
1,2,4-Trichlorobenzene 70 µg/L 79 (0.2%) SYR4
PFNA 77 (0.8%) UCMR-5
Bhc-Gamma 0.2000 µg/L 73 (0.3%) SYR4
1,1,2-Trichloroethane 5 µg/L 63 (0.2%) SYR4
Methoxychlor 40 µg/L 60 (0.2%) SYR4
Carbofuran 40 µg/L 56 (0.2%) SYR4
O-Dichlorobenzene 600 µg/L 53 (0.2%) SYR4
Dinoseb 7 µg/L 52 (0.2%) SYR4
Glyphosate 700 µg/L 46 (0.3%) SYR4
Lasso 2 µg/L 46 (0.2%) SYR4
Hfpo-Da 45 (0.5%) UCMR-5
Heptachlor 0.4000 µg/L 45 (0.2%) SYR4
Pfpes 44 (0.5%) UCMR-5
Endothall 100 µg/L 39 (0.3%) SYR4
2,4,5-TP 50 µg/L 37 (0.1%) SYR4
Oxamyl 200 µg/L 37 (0.1%) SYR4
Total Polychlorinated Biphenyls (PCB) 0.5000 µg/L 37 (0.2%) SYR4
Toxaphene 3 µg/L 35 (0.1%) SYR4
2,3,7,8-TCDD 0.000030 µg/L 18 (0.4%) SYR4
Pfda 13 (0.1%) UCMR-5
8:2 Fts 10 (0.1%) UCMR-5
Pfuna 6 (0.1%) UCMR-5
Pfhps 5 (0.1%) UCMR-5
Nfdha 4 (0%) UCMR-5
Pfdoa 4 (0%) UCMR-5
Adona 3 (0%) UCMR-5
4:2 Fts 2 (0%) UCMR-5
Pfmpa 2 (0%) UCMR-5
9Cl-PF3ONS 1 (0%) UCMR-5
Netfosaa 1 (0%) UCMR-5
Nmefosaa 1 (0%) UCMR-5
Pfmba 1 (0%) UCMR-5
0 (0%) UCMR-5
11Cl-PF3OUdS 0 (0%) UCMR-5
Pfeesa 0 (0%) UCMR-5
Pfta 0 (0%) UCMR-5
Pftrda 0 (0%) UCMR-5