Diquat in drinking water
839 active public water systems in 30 states had a Diquat violation in the past three years, and 45 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 Diquat and lists the water systems whose records include a related violation. It does not show measured levels.
Is Diquat 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.
Enter a ZIP code, town, or street address.
What it is and where it comes from
Diquat is a broad-spectrum contact herbicide used to control aquatic weeds, algae, and terrestrial vegetation. It remains in active use in the United States, applied directly to water bodies and irrigation canals. Diquat binds tightly to soil but can enter surface water directly during aquatic applications.
Health effects
Chronic exposure to diquat is associated with cataracts and kidney damage in animal studies. Acute high-level exposure causes gastrointestinal distress. EPA has not classified diquat as a human carcinogen. Individuals with kidney conditions may be at elevated risk from chronic exposure.
The standard and what a violation means
EPA limit: 0.02 mg/L (20 ppb).
Water systems with a Diquat 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 | 193 | 3% | 8 |
| Oklahoma | 105 | 8% | 0 |
| Oregon | 73 | 3% | 3 |
| Maine | 58 | 3% | 0 |
| Illinois | 52 | 1% | 15 |
| Colorado | 39 | 2% | 4 |
| Idaho | 37 | 2% | 3 |
| Connecticut | 34 | 1% | 1 |
| California | 28 | 0% | 1 |
| Indiana | 27 | 1% | 2 |
| Alabama | 26 | 5% | 0 |
| Alaska | 25 | 2% | 0 |
| Wyoming | 24 | 3% | 1 |
| Wisconsin | 19 | 0% | 0 |
| Nevada | 17 | 3% | 0 |
| Iowa | 16 | 1% | 0 |
| Arizona | 13 | 1% | 1 |
| Massachusetts | 12 | 1% | 1 |
| Montana | 9 | 0% | 0 |
| Washington | 8 | 0% | 1 |
| New Jersey | 6 | 0% | 2 |
| Minnesota | 5 | 0% | 2 |
| South Dakota | 3 | 0% | 0 |
| Michigan | 2 | 0% | 0 |
| North Dakota | 2 | 1% | 0 |
| New Mexico | 2 | 0% | 0 |
| Kansas | 1 | 0% | 0 |
| Kentucky | 1 | 0% | 0 |
| Ohio | 1 | 0% | 0 |
| Tennessee | 1 | 0% | 0 |
Largest water systems with a Diquat 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 |
|---|---|---|---|---|
|
Denver Water Board Denver County |
1,287,000 | 3 | 0 | |
|
Pittsburgh Water & Sewer Auth Allegheny County |
520,000 | 3 | 0 | |
|
Gilbert, Town of Gilbert · Maricopa County |
247,600 | 9 | 1 | |
|
Corona, City of Corona · Riverside County |
169,380 | 6 | 0 | |
|
City of Sunnyvale Sunnyvale · Santa Clara County |
157,566 | 5 | 0 | |
|
Epcor Agua Fria Surprise · Maricopa County |
128,040 | 5 | 0 | |
|
Inima USA / Aquaria LLC Dighton · Bristol County |
105,643 | 1 | 0 | |
|
GW Santa Cruz Water CO Maricopa · Pinal County |
84,000 | 7 | 0 | |
|
Flagstaff City of Flagstaff · Coconino County |
79,796 | 5 | 0 | |
|
Schaumburg Schaumburg · Cook County |
75,750 | 1 | 0 |
About this data
A system is counted once if any of its violations in the past three years involved Diquat, including monitoring and reporting lapses. Rules violated and status in the systems table are for the whole system, not Diquat 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.