EPA SDWIS ~155K water systems EPA + UCMR5

Interim Enhanced Surface Water Treatment Rule

Compiled by PlainWater Editorial, Drinking Water Quality Editorial Team · May 15, 2026

EPA SDWIS quarterly extract data for this analyte. Detection counts and health-based violation counts reflect the most recent federal release.

PlainWater home → About this data

EPA contaminant code: 0300

Total Violations

72,147

Systems Affected

2,920

Health-Based %

40%

Most Affected State

What this means

Interim Enhanced Surface Water Treatment Rule appears in EPA SDWIS with 72,147 recorded violations across 2,920 public water systems. Of those, 40% are classified as health-based, meaning the reading exceeded a federally enforceable Maximum Contaminant Level or a treatment-technique requirement rather than a monitoring or reporting lapse. Health-based violations are the subset that trigger formal corrective action and public notification, so the share is a useful signal of real-world exposure risk rather than paperwork drift. State-level concentration data is not consistently reported for this contaminant, so regional interpretation should lean on the system table below rather than state aggregates. Utilities listed below are ranked by cumulative violation count, so a higher rank reflects persistence in the record rather than a single spike; readers comparing systems should consider population served alongside violation count to gauge how many households were actually exposed.

Violation Type Split

Interim Enhanced Surface Water Treatment Rule violations broken down by EPA classification.

Health-based (40%) Monitoring/Reporting (60%)

Health-based violations indicate the contaminant exceeded an EPA Maximum Contaminant Level (MCL) or treatment-technique requirement; monitoring/reporting violations are procedural.

Most Affected Water Systems

System	State	Violations	Population
North Havre County Water Dist	MT	545	90
City of Toyah	TX	492	89
Cassie Water System	TX	475	106
Mohawk Valley School District	AZ	444	171
Adair Co RWD #5	OK	393	675
Delaware	OK	365	456
Fruitland Domestic WC	CO	351	335
City of Nome	TX	319	825
Specht Store	TX	311	170
South Mountain Restoration Ctr	PA	306	950
Wewoka Public Works Authority	OK	302	3,450
Otoe-Missouria Tribe	OK	297	250
Gypsy River Resort	TX	290	87
Kongiganak Water System	AK	285	547
Locust Grove	OK	284	1,600
Metropolitano	PR	275	1,077,332
Sardis Lake Water Authority	OK	259	307
Pawnee	OK	253	2,230
Auth of Boro of Charleroi	PA	234	27,000
Clearwater Water Dist	ID	232	80
Lamont	OK	232	417
Cedro Arriba	PR	232	5,482
Seven Hills Ranch	TX	232	801
Pine River Mdca	NM	228	44
Selawik Safewater Facility	AK	220	846
Trollers Cove Water Assn	OR	219	32
Alakanuk Water System	AK	217	570
City of Rose City	TX	217	664
Pinecrest Village MHP	PA	215	195
Pittsburg Co. RWD #14	OK	210	1,680

Drinking Water Guides

Understanding Water Quality Data

What EPA SDWIS tracks, how violations are classified, and what MCLs mean.

PFAS in Drinking Water

What forever chemicals are, EPA testing results, and 2024 standards.

Is My Water Safe?

How to assess your local water quality and when to take precautions.

Frequently Asked Questions

What is Interim Enhanced Surface Water Treatment Rule in drinking water? ▼

Interim Enhanced Surface Water Treatment Rule is a contaminant tracked by the EPA under the Safe Drinking Water Act. It has caused 72,147 violations across 2,920 public water systems nationwide. 40% of these violations are health-based, meaning the contaminant exceeded Maximum Contaminant Levels (MCLs) or treatment technique requirements.

How many water systems have Interim Enhanced Surface Water Treatment Rule violations? ▼

2,920 public water systems across the United States have at least one Interim Enhanced Surface Water Treatment Rule violation recorded in the EPA SDWIS database.

Are Interim Enhanced Surface Water Treatment Rule violations dangerous? ▼

40% of Interim Enhanced Surface Water Treatment Rule violations are health-based, meaning the contaminant level exceeded safe limits set by the EPA. Health-based violations require corrective action by the water system. Not all violations indicate immediate health risk, but they signal that water quality standards were not met.

Which state has the most Interim Enhanced Surface Water Treatment Rule violations? ▼

State-level breakdown data is not available for this contaminant.

Where does this contaminant data come from? ▼

All violation data comes from the EPA Safe Drinking Water Information System (SDWIS), which tracks compliance for all public water systems regulated under the Safe Drinking Water Act. SDWIS records violations including Maximum Contaminant Level (MCL) exceedances, treatment technique failures, and monitoring/reporting issues.

Data Sources

Contaminant violation data from the EPA Safe Drinking Water Information System (SDWIS). Violations are categorized as health-based (Maximum Contaminant Level exceedances, treatment technique failures) or monitoring/reporting violations.

Browse all → | Rankings →

Data sourced from EPA SDWIS and UCMR5 PFAS monitoring data. See our methodology for details. Retrieved and formatted by PlainWater Editorial

Disclaimer: This information is provided for informational purposes only and does not constitute professional advice. Data is sourced from the EPA Safe Drinking Water Information System (SDWIS). Consult a qualified professional before making decisions based on this data.

Read our methodology - how this data is sourced, computed, and verified.

Every figure on PlainWater is rendered directly from EPA SDWIS drinking-water data, no number is typed in by an editor. This page draws directly on EPA SDWIS data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.