Drinking Water Contaminants Guide
The EPA regulates over 90 contaminants in public drinking water under the Safe Drinking Water Act. Each contaminant has a maximum contaminant level (MCL) — the highest level allowed in drinking water. When a water system exceeds an MCL, it triggers a health-based violation.
Below are guides for the most commonly cited contaminants in drinking water violations. Each page explains where the contaminant comes from, what the health risks are, and what you can do if your water is affected.
| Contaminant | EPA Limit | Violations |
|---|---|---|
| Lead | 0.015 mg/L (action level) | 1,048 |
| Copper | 1.3 mg/L (action level) | 13,640 |
| Arsenic | 0.010 mg/L | 45,609 |
| Nitrate | 10 mg/L | 9,632 |
| Nitrite | 1 mg/L | 19,748 |
| Total Coliform Bacteria | Presence in >5% of monthly samples | 89,454 |
| E. coli | 0 (any detection is a violation) | 68,836 |
| Total Trihalomethanes (TTHM) | 0.080 mg/L (annual average) | 15,643 |
| Haloacetic Acids (HAA5) | 0.060 mg/L (annual average) | 76,767 |
| Fluoride | 4 mg/L | 6,570 |
| Barium | 2 mg/L | 120,970 |
| Mercury | 0.002 mg/L | 9,044 |
| Chromium | 0.1 mg/L | 8,576 |
| Selenium | 0.05 mg/L | 8,525 |
| Thallium | 0.002 mg/L | 1,836 |
| Beryllium | 0.004 mg/L | 7,422 |
| Cadmium | 0.005 mg/L | 16,458 |
| Cyanide | 0.2 mg/L | 521 |
| Antimony | 0.006 mg/L | 9,060 |