Contaminants · Systems with violations
The Most Common Drinking-Water Contaminants
Which contaminants and rules drive the most health-based violations across U.S. community water systems.
Lead leads "The Most Common Drinking-Water Contaminants" at 5,736 systems.
| # | State / item | Systems with violations |
|---|---|---|
| 1 | Lead 20M people served | 5,736 systems |
| 2 | Disinfection Byproducts (TTHM & HAA5) 34M people served | 4,670 systems |
| 3 | Bacteria & E. coli (Coliform) 12M people served | 2,462 systems |
| 4 | Radionuclides (Radium, Uranium, Gross Alpha) 2M people served | 791 systems |
| 5 | Arsenic 1M people served | 714 systems |
| 6 | Nitrate 3M people served | 636 systems |
| 7 | Fluoride 0M people served | 102 systems |
| 8 | Copper 0M people served | 2 systems |
Source: EPA Safe Drinking Water Information System (SDWIS) · 2026 Q1 refresh; violations since 2016