Water Quality in Duncan, OK: 30 Violations — Grade C
Grade C · Score 61/100 · 1 water system · Updated 2026-05-03
Duncan's water has moderate compliance issues. Residents in affected areas should consider filtration.
Data: EPA Safe Drinking Water Information System (SDWIS) Last verified: 2026-05-03
SDWIS records for Duncan, OK show 30 EPA violations documented for the local water supply — these span the full range of reportable events from health-based exceedances to monitoring and reporting lapses registered with the federal program.
Water Quality by ZIP Code in Duncan
Water quality varies across Duncan's 3 ZIP codes. Check your specific ZIP for detailed contaminant data.
| ZIP Code | Grade | Score | Violations | Health | |
|---|---|---|---|---|---|
| 73533 | C | 57 | 10 | 5 | View report → |
| 73534 | C | 63 | 10 | 5 | View report → |
| 73536 | C | 63 | 10 | 5 | View report → |
Violation Trend
EPA violations recorded for water systems serving Duncan.
Water Quality Overview
Duncan, Oklahoma receives a water quality grade of C with an overall score of 61 out of 100, based on EPA compliance data from the Safe Drinking Water Information System (SDWIS).
The 1 water system serving Duncan have accumulated 30 EPA violations, including 15 health-based violations. These violations are tracked across 3 ZIP codes serving approximately 23,000 people.
What Grade C Means
A grade of C indicates moderate compliance issues. Duncan's water systems have some violations that warrant attention. While the water may still be safe for most people, residents in affected ZIP codes should consider additional testing or filtration.
Lead Levels
Lead testing data for Duncan is currently being collected. The EPA requires all community water systems to test for lead under the Lead and Copper Rule.
With 77% of homes built before 1986, Duncan has a higher-than-average risk of lead from older plumbing. Lead solder was banned in 1986, and homes built before this date may have lead in pipes, solder joints, or fixtures.
Water Systems Serving Duncan
Duncan is served by 1 community water system regulated under the Safe Drinking Water Act. These systems collectively serve approximately 23,000 people across 3 ZIP codes.
Each water system is identified by a Public Water System ID (PWSID) and is required to:
- Test for over 90 regulated contaminants on a regular schedule
- Report results to the EPA and state regulators
- Issue an annual Consumer Confidence Report (CCR) to all customers
- Take corrective action when violations occur
The EPA has taken 30 enforcement actions against water systems serving Duncan. Enforcement actions range from informal compliance assistance to formal orders and penalties.
How to Check Your Water in Duncan
Enter your ZIP code on ZipCheckup to see your specific water system data, including contaminant levels, violation history, and safety scores
Request your CCR — your water utility must provide an annual Consumer Confidence Report with detailed test results for all monitored contaminants
Get a home test — certified kits cost $20–$50 and test for lead, bacteria, and common contaminants. Professional lab tests ($150–$400) cover a broader panel
Consider filtration — NSF-certified filters can remove specific contaminants. Reverse osmosis removes the broadest range; activated carbon is effective for chlorine and many organics
Check for advisories — monitor your local utility website and local news for boil water advisories or system alerts
Contaminants Detected in Duncan Water Systems
The following contaminants have been detected or caused violations across Duncan's water systems:
| Contaminant | Category | MCL | Violations | ZIPs Affected | Health-Based |
|---|---|---|---|---|---|
| Chlorite | Disinfection Byproducts | 1 mg/L | 15 | 3 | Yes |
| Haloacetic Acids (HAA5) | Disinfection Byproducts | 0.06 mg/L | 3 | 3 | Yes |
MCL = Maximum Contaminant Level (EPA enforceable standard). Health-based violations indicate levels that may pose direct health risks.
Violation Trend Over Time
Year-by-year EPA violations recorded for water systems serving Duncan:
| Year | Total Violations | Health-Based |
|---|---|---|
| 2023 | 3 | 3 |
| 2024 | 12 | 12 |
Violations have increased from 3 in 2023 to 12 in 2024. This trend warrants monitoring.
EPA Enforcement History
The EPA and state regulators have taken 10 enforcement actions against water systems serving Duncan. Recent actions:
| Date | Action Type |
|---|---|
| 2025-06-17 | State Informal Action |
| 2025-05-28 | State Informal Action |
| 2025-05-02 | State Informal Action |
| 2025-05-02 | State Informal Enforcement |
| 2025-04-15 | State Filed Suit |
| 2025-02-13 | State Order Extension |
| 2025-01-29 | State Informal Action |
| 2025-01-29 | State Informal Enforcement |
| 2024-12-23 | State Order Extension |
| 2024-10-21 | State Informal Action |
Enforcement actions range from informal compliance assistance to formal orders and penalties. The most recent action was on 2025-06-17.
Duncan vs. Nearby Oklahoma Cities
How Duncan's water quality compares to similar cities in Oklahoma:
| City | Grade | Violations | Systems | Population |
|---|---|---|---|---|
| Duncan | C | 30 | 1 | 23,000 |
| Fort Sill | A | 4 | 1 | 23,000 |
| Yukon | B | 22 | 3 | 23,036 |
| Owasso | A | 22 | 2 | 23,176 |
Water Quality by ZIP Code in Duncan
Water quality varies across Duncan's ZIP codes. The table below shows the worst-scoring and best-scoring areas:
Common Questions About Duncan Water
These are the most common questions residents search for about water quality in Duncan, Oklahoma:
Is Duncan water hard or soft? Water hardness varies by source. Duncan's 1 water system uses a single source. Check your ZIP code report for specific hardness data.
Can I drink Duncan tap water? Duncan's water receives a grade of C (61/100). There are 15 health-based violations — consider filtration.
What is the best water filter for Duncan? A NSF/ANSI 53-certified filter for lead removal is a good general choice. See our Water Filter Matcher for personalized recommendations.
Duncan vs. Oklahoma Average
Understanding how Duncan compares to the broader Oklahoma average helps contextualize your local water quality. Factors like water source, treatment methods, and infrastructure age all contribute to differences between cities in the same state.
To see how individual neighborhoods compare, check the ZIP code reports below — water quality can vary significantly even within Duncan.
ZIP Codes in Duncan
Duncan spans 3 ZIP codes. The ZIP with the lowest water quality score is 73533. Each ZIP code has its own water quality profile based on the specific water system serving that area. Check each ZIP code for detailed contaminant data, violation history, and system information.
Data Sources
- Water quality: EPA Safe Drinking Water Information System (SDWIS)
- Lead/copper: EPA Lead and Copper Rule sampling data
- Radon: EPA Map of Radon Zones
- Enforcement: EPA ECHO database
- Filter recommendations: NSF/ANSI certified products
Updated daily.