Nitrite in drinking water
1,821 active public water systems in 33 states had a Nitrite violation in the past three years, and 48 have one that is still unresolved.
You are on Tapcensus, an independent guide to the EPA compliance records of every public water system in the United States. This page explains Nitrite and lists the water systems whose records include a related violation. It does not show measured levels.
Is Nitrite in the records for your water system?
Enter a ZIP code, town, or street address to see the water systems that serve your area, their status, and which rules and contaminants appear in their violations.
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What it is and where it comes from
Nitrite (NO₂) enters water from fertilizer runoff, septic systems, and natural mineral deposits. Unlike nitrate, nitrite acts very quickly in the body — it converts hemoglobin to methemoglobin, which cannot carry oxygen. Nitrite can also form in distribution systems through microbial nitrification when chloramine disinfection breaks down.
Health effects
Methemoglobinemia ('blue baby syndrome') in infants under 6 months: reduced oxygen delivery to tissues can be life-threatening. Pregnant women and people with glucose-6-phosphate dehydrogenase (G6PD) deficiency are also at elevated risk. Adults are generally less susceptible due to more effective methemoglobin reduction.
The standard and what a violation means
EPA limit: 1 mg/L as nitrogen (NO₂-N).
Water systems with a Nitrite violation, by state
Active public water systems that reported at least one related violation to EPA in the past three years. Each state links to the list of its affected systems.
| State | Systems with violations, 3 yr | Share of active systems | Unresolved |
|---|---|---|---|
| Pennsylvania | 755 | 10% | 14 |
| Illinois | 213 | 4% | 7 |
| Connecticut | 90 | 4% | 2 |
| California | 82 | 1% | 0 |
| West Virginia | 71 | 9% | 2 |
| Idaho | 64 | 3% | 2 |
| Indiana | 53 | 1% | 0 |
| Mississippi | 52 | 4% | 0 |
| Iowa | 50 | 3% | 13 |
| Oklahoma | 43 | 3% | 0 |
| New York | 38 | 0% | 0 |
| Texas | 32 | 0% | 0 |
| Wisconsin | 32 | 0% | 1 |
| Arizona | 29 | 2% | 1 |
| Nevada | 28 | 5% | 0 |
| Michigan | 25 | 0% | 0 |
| New Jersey | 23 | 1% | 0 |
| Washington | 19 | 0% | 0 |
| Massachusetts | 17 | 1% | 2 |
| Rhode Island | 17 | 4% | 0 |
| North Carolina | 15 | 0% | 0 |
| New Mexico | 13 | 1% | 0 |
| Oregon | 12 | 0% | 0 |
| Colorado | 11 | 0% | 0 |
| Wyoming | 10 | 1% | 3 |
| Maine | 8 | 0% | 0 |
| Alabama | 5 | 1% | 0 |
| New Hampshire | 4 | 0% | 0 |
| Montana | 3 | 0% | 0 |
| Utah | 3 | 0% | 0 |
| Minnesota | 2 | 0% | 0 |
| District of Columbia | 1 | 7% | 0 |
| Ohio | 1 | 0% | 1 |
Largest water systems with a Nitrite violation
The ten biggest systems, by people served, whose records include a related violation in the past three years.
| System | Serves | Status | Rules violated, 3 yr | Unresolved |
|---|---|---|---|---|
|
Corona, City of Corona · Riverside County |
169,380 | 6 | 0 | |
|
City of Sunnyvale Sunnyvale · Santa Clara County |
157,566 | 5 | 0 | |
|
Jalama Beach Park Santa Barbara County |
120,017 | 1 | 0 | |
|
Lca Wlsa Central Division Lehigh County |
47,693 | 2 | 0 | |
|
Isu Ames · Story County |
42,000 | 1 | 0 | |
|
Riverhead Water District Riverhead (t) · Suffolk County |
35,000 | 1 | 0 | |
|
West Bend Waterworks West Bend · Washington County |
32,149 | 5 | 0 | |
|
Elk Grove Village Elk Grove · Cook County |
31,802 | 4 | 1 | |
|
Wannacomet Water Company Nantucket · Nantucket County |
27,703 | 7 | 2 | |
|
Reading Water Department (mwra) Reading · Middlesex County |
26,262 | 1 | 0 |
About this data
A system is counted once if any of its violations in the past three years involved Nitrite, including monitoring and reporting lapses. Rules violated and status in the systems table are for the whole system, not Nitrite alone. Counts cover active systems in all 50 states and the District of Columbia.
Source: the U.S. EPA's Enforcement and Compliance History Online system (ECHO), which publishes the federal Safe Drinking Water Information System. EPA's terms and values are shown as published. The records are from EPA's data refresh of Oct 7, 2026; EPA refreshes this data quarterly, and states report to EPA with a lag of three to six months, so the newest violations may not appear yet.