Chlorine (MRDL) in drinking water
4,173 active public water systems in 41 states had a Chlorine (MRDL) violation in the past three years, and 432 had one in the latest quarter of EPA's data.
You are on Tapcensus, an independent guide to the EPA compliance records of every public water system in the United States. This page explains Chlorine (MRDL) and lists the water systems whose records include a related violation. It does not show measured levels.
Is Chlorine (MRDL) 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
This entry tracks violations of the Maximum Residual Disinfectant Level (MRDL) for chlorine — meaning too much disinfectant residual in the distribution system, not too little. Chlorine is added to water to kill pathogens, but excess residual can react with organic matter to form disinfection byproducts.
Health effects
Acute high-dose exposure to chlorinated water can cause eye and nose irritation, stomach discomfort, and nausea. Chronic exposure above the MRDL is primarily a concern because elevated chlorine accelerates formation of trihalomethanes and haloacetic acids, which are associated with increased cancer risk over time.
The standard and what a violation means
EPA limit: MRDL: 4.0 mg/L as an annual average.
Water systems with a Chlorine (MRDL) 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 | In violation, latest quarter |
|---|---|---|---|
| Texas | 971 | 13% | 0 |
| Pennsylvania | 429 | 6% | 66 |
| Oklahoma | 293 | 23% | 36 |
| Arizona | 275 | 16% | 24 |
| Colorado | 230 | 10% | 38 |
| Kansas | 226 | 24% | 22 |
| Illinois | 203 | 4% | 22 |
| Mississippi | 171 | 14% | 0 |
| Alaska | 152 | 11% | 56 |
| North Carolina | 150 | 3% | 18 |
| West Virginia | 135 | 18% | 20 |
| Virginia | 118 | 4% | 22 |
| New Jersey | 112 | 3% | 18 |
| New Mexico | 103 | 9% | 4 |
| Idaho | 101 | 5% | 19 |
| Minnesota | 72 | 1% | 6 |
| California | 57 | 1% | 12 |
| Michigan | 51 | 0% | 6 |
| Washington | 44 | 1% | 7 |
| South Dakota | 33 | 5% | 5 |
| North Dakota | 32 | 8% | 5 |
| Tennessee | 29 | 4% | 4 |
| Arkansas | 25 | 3% | 0 |
| Connecticut | 22 | 1% | 6 |
| Wyoming | 22 | 3% | 0 |
| Nevada | 17 | 3% | 0 |
| New Hampshire | 13 | 1% | 6 |
| South Carolina | 13 | 1% | 1 |
| Montana | 10 | 0% | 2 |
| New York | 9 | 0% | 0 |
| Wisconsin | 9 | 0% | 3 |
| Rhode Island | 8 | 2% | 0 |
| Massachusetts | 7 | 0% | 0 |
| Oregon | 7 | 0% | 3 |
| Vermont | 7 | 1% | 1 |
| Utah | 6 | 1% | 0 |
| Louisiana | 3 | 0% | 0 |
| Nebraska | 3 | 0% | 0 |
| Iowa | 2 | 0% | 0 |
| Ohio | 2 | 0% | 0 |
| District of Columbia | 1 | 7% | 0 |
Largest water systems with a Chlorine (MRDL) 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 |
|---|---|---|---|---|
|
Metro Water Services Nashville · Davidson County |
789,969 | 2 | 0 | |
|
City of Garland Dallas County |
248,822 | 2 | 0 | |
|
Trenton Water Works Ewing Twp, Hamilton Twp, Hopewell Twp.1106- and 2 more · Mercer County |
217,000 | 8 | 2 | |
|
Wvawc-Kanawha Valley Dist Charleston · Kanawha County |
209,283 | 3 | 0 | |
|
Avondale City of Avondale · Maricopa County |
96,130 | 2 | 0 | |
|
Epcor San Tan Johnson Ranch · Pinal County |
87,435 | 3 | 0 | |
|
City of Baytown Harris County |
86,004 | 1 | 0 | |
|
GW Santa Cruz Water CO Maricopa · Pinal County |
84,000 | 7 | 0 | |
|
Burlington, City of Burlington · Alamance County |
61,365 | 2 | 0 | |
|
Harrisonburg, City of Harrisonburg City · County |
61,000 | 1 | 0 |
About this data
A system is counted once if any of its violations in the past three years involved Chlorine (MRDL), including monitoring and reporting lapses. Rules violated and status in the systems table are for the whole system, not Chlorine (MRDL) 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.