Interim Enhanced Surface Water Treatment Rule in drinking water
952 active public water systems in 43 states had a Interim Enhanced Surface Water Treatment Rule violation in the past three years, and 173 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 Interim Enhanced Surface Water Treatment Rule and lists the water systems whose records include a related violation. It does not show measured levels.
Is Interim Enhanced Surface Water Treatment Rule 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
The Interim Enhanced Surface Water Treatment Rule (IESWTR), finalized in 1998, strengthened protections for systems serving 10,000 or more people by tightening turbidity limits and requiring Cryptosporidium removal. It was an intermediate step between the original SWTR and the Long-Term Enhanced SWTRs.
Health effects
Violations indicate failure to meet treatment technique requirements that reduce exposure to Cryptosporidium, Giardia, and other microbial pathogens. Cryptosporidium poses the greatest risk to immunocompromised individuals, infants, and the elderly, and can cause severe or fatal illness in vulnerable populations.
The standard and what a violation means
EPA limit: Treatment technique — no numeric MCL; compliance means meeting turbidity limits (0.3 NTU in 95% of monthly samples) and Cryptosporidium removal benchmarks.
Water systems with a Interim Enhanced Surface Water Treatment Rule 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 |
|---|---|---|---|
| Colorado | 170 | 8% | 30 |
| Pennsylvania | 92 | 1% | 17 |
| Texas | 90 | 1% | 3 |
| Alaska | 89 | 7% | 31 |
| Oregon | 80 | 3% | 20 |
| Oklahoma | 69 | 5% | 14 |
| West Virginia | 49 | 6% | 4 |
| Minnesota | 33 | 1% | 2 |
| Arizona | 30 | 2% | 5 |
| Tennessee | 29 | 4% | 23 |
| Missouri | 24 | 1% | 3 |
| New Mexico | 23 | 2% | 4 |
| Illinois | 20 | 0% | 0 |
| Idaho | 18 | 1% | 6 |
| California | 15 | 0% | 1 |
| Louisiana | 15 | 1% | 2 |
| Ohio | 14 | 0% | 0 |
| Kentucky | 12 | 3% | 0 |
| New York | 10 | 0% | 0 |
| North Carolina | 9 | 0% | 3 |
| Kansas | 8 | 1% | 1 |
| Wyoming | 8 | 1% | 2 |
| Arkansas | 5 | 1% | 0 |
| Montana | 5 | 0% | 1 |
| New Jersey | 5 | 0% | 0 |
| Indiana | 4 | 0% | 0 |
| Washington | 4 | 0% | 0 |
| Maryland | 2 | 0% | 0 |
| Maine | 2 | 0% | 0 |
| New Hampshire | 2 | 0% | 0 |
| Rhode Island | 2 | 0% | 0 |
| South Dakota | 2 | 0% | 0 |
| Virginia | 2 | 0% | 0 |
| Alabama | 1 | 0% | 0 |
| Connecticut | 1 | 0% | 0 |
| Florida | 1 | 0% | 0 |
| Georgia | 1 | 0% | 0 |
| Hawaii | 1 | 1% | 0 |
| Iowa | 1 | 0% | 1 |
| Massachusetts | 1 | 0% | 0 |
| Michigan | 1 | 0% | 0 |
| Nebraska | 1 | 0% | 0 |
| Utah | 1 | 0% | 0 |
Largest water systems with a Interim Enhanced Surface Water Treatment Rule 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 |
|---|---|---|---|---|
|
City of Houston Harris County |
2,970,543 | 1 | 0 | |
|
Chicago Cook County |
2,721,308 | 4 | 0 | |
|
Philadelphia Water Department Philadelphia County |
1,600,000 | 1 | 0 | |
|
Denver Water Board Denver County |
1,287,000 | 3 | 0 | |
|
Pittsburgh Water & Sewer Auth Allegheny County |
520,000 | 3 | 0 | |
|
Metropolitan District Commission Berlin, Bloomfield, Cromwell and 14 more · Hartford County |
390,887 | 1 | 0 | |
|
New Orleans Carrollton Water Works Orleans County |
334,903 | 1 | 0 | |
|
City of Laredo Webb County |
260,046 | 4 | 0 | |
|
Gilbert, Town of Gilbert · Maricopa County |
247,600 | 9 | 1 | |
|
Norfolk, City of Norfolk City · County |
234,220 | 1 | 0 |
About this data
A system is counted once if any of its violations in the past three years involved Interim Enhanced Surface Water Treatment Rule, including monitoring and reporting lapses. Rules violated and status in the systems table are for the whole system, not Interim Enhanced Surface Water Treatment Rule 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.