Groundwater Rule (GWR) in drinking water
2,821 active public water systems in 43 states had a Groundwater Rule (GWR) violation in the past three years, and 1,720 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 Groundwater Rule (GWR) and lists the water systems whose records include a related violation. It does not show measured levels.
Is Groundwater Rule (GWR) 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
The 2006 GWR requires regular sanitary surveys of groundwater systems and targeted corrective action when fecal indicators are found in source water. Systems with significant deficiencies must provide 4-log virus treatment (99.99% removal/inactivation) or fix the deficiency.
Health effects
Protects against enteric viruses, which can contaminate groundwater via cracked well casings, failing septic systems, or animal waste. Viruses persist longer in groundwater than in surface water. Hepatitis A and norovirus are the primary pathogens of concern.
The standard and what a violation means
EPA limit: Treatment technique: 4-log virus treatment required when source water has fecal indicators or significant sanitary deficiencies.
Water systems with a Groundwater Rule (GWR) 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 |
|---|---|---|---|
| Pennsylvania | 968 | 13% | 256 |
| Louisiana | 250 | 21% | 250 |
| West Virginia | 208 | 27% | 94 |
| New Mexico | 186 | 16% | 186 |
| Indiana | 141 | 4% | 138 |
| Missouri | 140 | 5% | 59 |
| Arizona | 107 | 6% | 106 |
| Idaho | 107 | 5% | 95 |
| Alaska | 82 | 6% | 81 |
| Oregon | 71 | 3% | 32 |
| Colorado | 46 | 2% | 46 |
| Nevada | 46 | 8% | 46 |
| New York | 46 | 1% | 6 |
| Montana | 45 | 2% | 18 |
| California | 35 | 0% | 33 |
| Connecticut | 32 | 1% | 28 |
| Wyoming | 31 | 4% | 30 |
| Kansas | 26 | 3% | 11 |
| Mississippi | 23 | 2% | 23 |
| Washington | 22 | 0% | 14 |
| Wisconsin | 20 | 0% | 20 |
| Illinois | 19 | 0% | 19 |
| Massachusetts | 19 | 1% | 17 |
| New Jersey | 19 | 1% | 3 |
| Utah | 18 | 2% | 18 |
| Minnesota | 16 | 0% | 11 |
| Ohio | 16 | 0% | 15 |
| Texas | 16 | 0% | 15 |
| Michigan | 10 | 0% | 10 |
| New Hampshire | 9 | 0% | 9 |
| District of Columbia | 7 | 50% | 7 |
| Virginia | 7 | 0% | 2 |
| Rhode Island | 6 | 1% | 2 |
| Maryland | 5 | 0% | 5 |
| Kentucky | 4 | 1% | 2 |
| South Dakota | 4 | 1% | 4 |
| Tennessee | 4 | 1% | 0 |
| Iowa | 3 | 0% | 2 |
| Arkansas | 2 | 0% | 2 |
| Nebraska | 2 | 0% | 2 |
| Delaware | 1 | 0% | 1 |
| North Carolina | 1 | 0% | 1 |
| North Dakota | 1 | 0% | 1 |
Largest water systems with a Groundwater Rule (GWR) 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 |
|---|---|---|---|---|
|
Aqua PA Main System Montgomery County |
822,600 | 6 | 0 | |
|
Lca Allentown Division Lehigh County |
118,000 | 3 | 0 | |
|
Rio Rancho Water & WW Services Rio Rancho · Sandoval County |
107,350 | 2 | 1 | |
|
Medford Water Commission Jackson County |
106,068 | 3 | 0 | |
|
ST Charles County Pwsd 2 St. Charles County |
100,587 | 1 | 0 | |
|
Carmel Water Department Carmel · Hamilton County |
99,927 | 1 | 0 | |
|
Tangipahoa Parish Water District Tangipahoa County |
75,873 | 2 | 1 | |
|
North Wales Water Authority Montgomery County |
72,496 | 2 | 0 | |
|
State College Boro Water Auth Centre County |
72,000 | 5 | 0 | |
|
Lake Havasu City of Lake Havasu City · Mohave County |
54,610 | 2 | 0 |
About this data
A system is counted once if any of its violations in the past three years involved Groundwater Rule (GWR), including monitoring and reporting lapses. Rules violated and status in the systems table are for the whole system, not Groundwater Rule (GWR) 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.