Is Duncan, OK Tap Water Safe to Drink?
Graded D+, with 1 unresolved violation on record. See what was cited — and what it means for your tap. What to do next ↓
50.2/100
waterverge.com Duncan, OK — Water Quality Report
Duncan's drinking water received a grade of D+ (50.2 out of 100), indicating poor water quality. The city's 1 water system serves approximately 23,000 residents using surface water.
Lead levels were measured at 0.0 ppb (90th percentile), well within EPA limits. UCMR 5 testing detected 5 PFAS compounds in the water supply.
The system has 167 violations on record, including 150 health-based violations. 1 remains unresolved.
What to know about Duncan's water
Duncan ranks #209 out of 358 cities in Oklahoma for water quality, placing it below average in the state.
The city draws from surface water sources, which are more susceptible to seasonal runoff and agricultural contamination, requiring extensive multi-barrier treatment including coagulation, filtration, and disinfection.
PFAS compounds were detected in testing, though levels remain within current EPA limits. Residents seeking extra precaution may consider an activated carbon or reverse osmosis filter.
Hexavalent chromium (chromium-6) was detected at 0.46 µg/L in UCMR 3 testing. While below California's 10 µg/L limit and with no federal MCL set, residents sensitive to this contaminant may consider reverse osmosis filtration.
The system has seen 10 violations in the past five years, suggesting a pattern of compliance challenges that residents should monitor closely.
Water quality score
See methodology →Is Duncan, OK water safe to drink?
Duncan's tap water meets most EPA standards but has areas that warrant attention. With a grade of D+ (50.2/100), some contaminant levels or compliance issues suggest that residents may benefit from additional filtration. The city's 1 water system serves approximately 23,000 residents using surface water (rivers, lakes, or reservoirs).
Recent water quality updates for Duncan
A timeline of significant water quality events, violations, and data updates.
Detected at levels within current EPA limits. PFAS persist indefinitely in the environment.
Latest EPA compliance and testing data incorporated into Duncan's water quality assessment. Grade: D+ (50.2/100).
Contaminants: Chloramine.
Contaminants: Revised Total Coliform Rule, Chloramine.
1 health-based. Contaminants: CARBON, TOTAL.
Federal disaster declaration (FEMA DR-4274). Flood event — may have impacted local water infrastructure.
Key contaminant findings
Based on the most recent EPA sampling data for Duncan's water supply.
Well within EPA limits.
Detected but within current EPA limits. PFAS do not break down in the environment and can accumulate in the body over time. An activated carbon filter can reduce exposure.
PFAS "forever chemicals" detected
UCMR 5 testing found 5 PFAS compounds in Duncan's water supply. PFAS are synthetic chemicals that persist indefinitely in the environment and the human body.
Violation history
Duncan's water system has 167 total violations on record, including 150 health-based violations. 1 remain unresolved. 10 violations were issued in the last 5 years.
Flood & environmental risk
Stephens County has experienced 4 federally declared disasters since 1983. Flooding and severe storms can overwhelm water treatment plants, cause sewage overflows, and introduce agricultural runoff, bacteria, and sediment into drinking water supplies. Local water sources include Lake Humphreys Near Duncan.
Where does Duncan's water come from?
Duncan's drinking water comes from surface water (rivers, lakes, or reservoirs), supplied by 1 water system serving approximately 23,000 people. Surface water sources are more susceptible to contamination from runoff, industrial discharge, and algal blooms, requiring extensive treatment. Nearby water bodies include Lake Humphreys Near Duncan (lake).
What Duncan residents can do
Your water utility is required to publish an annual Consumer Confidence Report (CCR) with detailed testing results. Ask for the latest copy or check your utility's website.
Duncan's area has a history of flooding. After severe weather, watch for boil water advisories from your local utility.
Data: EPA SDWIS, UCMR 5 (PFAS), FEMA, NOAA. Last updated May 2026.
Top contaminants to know
View all ↓Forever chemicals overview
National PFAS report →Violation summary
Violations & advisories
Top industrial polluters within 10 miles of Duncan
Industrial polluters nearby
Reported releases to surface water by facilities near Duncan, ranked by pounds discharged annually.
| Facility | Top chemical | To surface water (lbs/yr) | Distance |
|---|---|---|---|
HALLIBURTON MANUFACTURING & LEASING CO LLC DUNCAN, OK73536 | — | — | 0.3 mi |
DCP MIDSTREAM LP/SHOLEM GAS PLANT DUNCAN, OK73533 | — | — | 1.9 mi |
DUNCAN #2 BATCH PLANT DUNCAN, OK73533 | — | — | 1.2 mi |
HALLIBURTON DUNCAN FIELD CAMP DUNCAN, OK73533 | — | — | 1.3 mi |
SENSIA LLC DUNCAN, OK73533 | — | — | 1.9 mi |
Source: EPA Toxic Release Inventory (TRI) 2023
Drought conditions
D1 — moderate droughtStephens County is currently in D1 (moderate drought) per the U.S. Drought Monitor (week of May 5, 2026). Drought can elevate disinfection-byproduct (TTHM/HAA5) levels and taste/odor issues as utilities draw from lower reservoirs.
Source: U.S. Drought Monitor, updated weekly by NDMC, USDA, and NOAA.
Flood & disaster history
Stephens County has experienced 4 federally declared disasters since 1983. Flooding and severe weather can compromise water treatment infrastructure and introduce contaminants into drinking water supplies.
Recommended water filters
Based on contaminants detected in Duncan's water supply, we recommend the following filter types.
Full contaminants report
| Contaminant | Detected Level | EPA Limit | Unit | Category | Status |
|---|---|---|---|---|---|
| Lead (90th percentile) LeadHeavy Metal A toxic heavy metal that can leach into drinking water from older pipes, solder, and fixtures. No amount of lead in water is considered safe. Health EffectsBrain and nervous system damage in children, kidney damage, high blood pressure, and reproductive problems in adults. EPA Limit15 ppb action level Common SourcesCorrosion of lead pipes, lead solder, brass faucets, and household plumbing. | 0.0 | 15 | ppb | Inorganic | Safe |
| 11Cl-PF3OUdS | ND | HI | µg/L | PFAS | Not Detected |
| 4:2 FTS | ND | HI | µg/L | PFAS | Not Detected |
| 6:2 FTS 6:2 FTSPFAS A fluorotelomer sulfonate commonly found at sites contaminated with aqueous film-forming foam (AFFF) used in firefighting. Health EffectsPotential liver toxicity and endocrine disruption. Less studied but identified as a contaminant of concern. EPA LimitNo individual MCL (not yet regulated) Common SourcesFirefighting foam (AFFF), airports, military bases, and industrial facilities. | ND | HI | µg/L | PFAS | Not Detected |
| 8:2 FTS | ND | HI | µg/L | PFAS | Not Detected |
| 9Cl-PF3ONS | ND | HI | µg/L | PFAS | Not Detected |
| ADONA | ND | HI | µg/L | PFAS | Not Detected |
| HFPO-DA HFPO-DA (GenX)PFAS A replacement for PFOA in manufacturing, marketed as safer but still a persistent "forever chemical." Also known as GenX. Health EffectsLiver and kidney effects, reproductive toxicity, immune system effects, and potential cancer risk. EPA Limit10 ppt MCL Common SourcesFluoropolymer manufacturing (used as PFOA replacement), industrial wastewater discharge. | ND | 0.01 | µg/L | PFAS | Not Detected |
| lithium LithiumInorganic A naturally occurring alkali metal found in groundwater. Monitored under UCMR 5 to assess occurrence in drinking water. Health EffectsKidney effects at high doses. Low-level exposure effects under study; some research suggests neurological effects. EPA LimitNo MCL (monitoring only under UCMR 5) Common SourcesNatural mineral deposits, geothermal water, and industrial discharge. | 14.200 | HI | µg/L | PFAS | Detected |
| NEtFOSAA | ND | HI | µg/L | PFAS | Not Detected |
| NFDHA | ND | HI | µg/L | PFAS | Not Detected |
| NMeFOSAA | ND | HI | µg/L | PFAS | Not Detected |
| PFBA PFBAPFAS One of the shortest-chain PFAS compounds. Very mobile in water and difficult to remove with standard filtration. Health EffectsThyroid effects, potential developmental toxicity. Shorter half-life in body than long-chain PFAS. EPA LimitNo individual MCL (not yet regulated) Common SourcesDegradation of longer-chain PFAS, industrial discharge, and firefighting foam. | 0.007 | HI | µg/L | PFAS | Detected |
| PFBS PFBSPFAS A short-chain PFAS used as a replacement for PFOS. While it clears the body faster than long-chain PFAS, it still persists in the environment. Health EffectsThyroid effects, reproductive and developmental toxicity, kidney effects. EPA LimitPart of Hazard Index (1.0) Common SourcesIndustrial discharge, firefighting foam, and as a replacement chemical in manufacturing. | ND | HI | µg/L | PFAS | Not Detected |
| PFDA | ND | HI | µg/L | PFAS | Not Detected |
| PFDoA | ND | HI | µg/L | PFAS | Not Detected |
| PFEESA | ND | HI | µg/L | PFAS | Not Detected |
| PFHpA PFHpAPFAS A medium-chain PFAS compound found in various environmental samples. Less studied than PFOA/PFOS but still considered a contaminant of concern. Health EffectsLiver effects, potential developmental toxicity, and endocrine disruption. EPA LimitPart of Hazard Index (1.0) Common SourcesDegradation of longer-chain PFAS, industrial discharge, and contaminated water sources. | 0.003 | HI | µg/L | PFAS | Detected |
| PFHpS | ND | HI | µg/L | PFAS | Not Detected |
| PFHxA PFHxAPFAS A short-chain PFAS replacement chemical widely used after manufacturers phased out longer-chain PFAS. Very commonly detected in water. Health EffectsLiver and kidney effects, potential thyroid disruption. Considered less toxic than long-chain PFAS but still persistent. EPA LimitNo individual MCL (not yet regulated) Common SourcesIndustrial processes, firefighting foam (AFFF), food packaging, and textile treatment. | 0.003 | HI | µg/L | PFAS | Detected |
| PFHxS PFHxSPFAS A medium-chain PFAS found in firefighting foam and consumer products. It has a long half-life in the human body, similar to long-chain PFAS. Health EffectsImmune system effects, thyroid disruption, and potential reproductive and developmental harm. EPA LimitPart of Hazard Index (1.0) Common SourcesFirefighting foam (AFFF), waterproof textiles, food packaging, and industrial discharge. | ND | HI | µg/L | PFAS | Not Detected |
| PFMBA | ND | HI | µg/L | PFAS | Not Detected |
| PFMPA | ND | HI | µg/L | PFAS | Not Detected |
| PFNA PFNAPFAS A long-chain PFAS compound used in manufacturing fluoropolymers. It bioaccumulates in the body and is very persistent in the environment. Health EffectsDevelopmental effects, liver toxicity, immune suppression, and potential cancer risk. EPA LimitPart of Hazard Index (1.0) Common SourcesFluoropolymer manufacturing, industrial emissions, and contaminated water sources. | ND | HI | µg/L | PFAS | Not Detected |
| PFOA PFOAPFAS A long-chain PFAS ("forever chemical") once widely used in nonstick coatings and firefighting foam. It persists in the body and environment for years. Health EffectsLinked to kidney and testicular cancer, thyroid disease, elevated cholesterol, and reproductive issues. EPA Limit4.0 ppt MCL Common SourcesIndustrial discharge, firefighting foam (AFFF), nonstick cookware manufacturing, and contaminated groundwater. | ND | 0.004 | µg/L | PFAS | Not Detected |
| PFOS PFOSPFAS A long-chain PFAS compound historically used in stain-resistant coatings and firefighting foam. One of the most studied and persistent PFAS chemicals. Health EffectsLiver damage, immune system suppression, thyroid disruption, increased cholesterol, and potential cancer risk. EPA Limit4.0 ppt MCL Common SourcesFirefighting foam (AFFF), industrial sites, stain-resistant fabric treatments, and contaminated groundwater. | ND | 0.004 | µg/L | PFAS | Not Detected |
| PFPeA PFPeAPFAS A short-chain PFAS compound commonly detected in drinking water. One of the most frequently found PFAS in UCMR 5 monitoring. Health EffectsLess studied than PFOA/PFOS. Potential liver and thyroid effects. Research is ongoing. EPA LimitNo individual MCL (not yet regulated) Common SourcesIndustrial discharge, firefighting foam degradation, and consumer products. | 0.004 | HI | µg/L | PFAS | Detected |
| PFPeS | ND | HI | µg/L | PFAS | Not Detected |
| PFTA | ND | HI | µg/L | PFAS | Not Detected |
| PFTrDA | ND | HI | µg/L | PFAS | Not Detected |
| PFUnA | ND | HI | µg/L | PFAS | Not Detected |
Lead level trend (90th percentile)
See how Duncan compares by contaminant
Explore where Duncan ranks among all Oklahoma cities for specific contaminants.
Water source & infrastructure
Where Duncan's water comes from
Duncan's drinking water comes primarily from surface water sources such as rivers, lakes, or reservoirs.
Surface water systems require multi-stage treatment including coagulation, sedimentation, filtration, and disinfection to meet EPA Safe Drinking Water Act standards.
These sources can be impacted by seasonal changes, stormwater runoff, upstream agriculture, and industrial discharge.
The system is operated by local government ownership and serves approximately 23,000 people through 1 water system.
Water bodies near Duncan
Duncan is located near 1 notable water body. As a surface water system, these water bodies may directly influence the city's drinking water supply.
Water systems serving Duncan
| System Name | PWSID | Population | Source |
|---|---|---|---|
| DUNCAN PUBLIC UTILITIES AUTHORITY | OK1010809 | 23,000 | SW |
How Duncan compares
Full Oklahoma rankings →Duncan's score of 50.2/100 is above the average of 45/100 among major Oklahoma cities. It outscores 9 of 10 nearby cities.
Nearby cities
View Oklahoma rankings →About Duncan, OK
Wikipedia →Duncan is a city in and the county seat of Stephens County, Oklahoma, United States. Its population was 22,310 at the 2020 census. Centrally located in Stephens County, Duncan became the county seat after Oklahoma achieved statehood in 1907. Oil wells opened in Stephens County in 1918 and led to rapid development. Cotton was a dominant crop until the Dust Bowl brought its decline, but cattle remain an important part of the economy. The Chisholm Trail passed to the east of Duncan prior to the town's founding, which is home to the Chisholm Trail Heritage Center.
Learn more about your water
Guides and resources related to Duncan's water quality findings.
Explore water quality across Stephens
Frequently asked questions
Is Duncan, OK tap water safe to drink?
Duncan's water quality earned a grade of D+ (50.2/100). Significant issues have been found. A water filter is strongly recommended. The city ranks #209 out of 358 cities tested in Oklahoma.
What contaminants are in Duncan's water?
Lead was measured at 0.0 ppb (90th percentile). 5 PFAS compounds were detected. 167 violations are on record.
How is Duncan's water quality grade calculated?
The grade is based on four factors: violation history (40%), lead and copper levels (25%), PFAS contamination (25%), and regulatory compliance (10%). The score is also adjusted based on how complete the available data is. See our methodology page for full details.
Do I need a water filter in Duncan?
PFAS compounds have been detected. A filter with activated carbon can help reduce exposure.
Where does Duncan's water come from?
Duncan's water is sourced from Surface water. The city has 1 water system serving approximately 23,000 residents.
What health violations has Duncan's water system had?
Duncan has 150 health-based violations on record. The most recent violation was recorded in November 2025. Health-based violations mean the water exceeded EPA maximum contaminant levels (MCLs) for a regulated substance. 1 violation remains unresolved.
Why does Duncan have so many PFAS compounds in its water?
5 different PFAS "forever chemical" compounds were detected in Duncan's water supply during UCMR 5 testing. PFAS contamination often originates from proximity to military installations (AFFF firefighting foam), airports, industrial manufacturing sites, or wastewater treatment facilities. While detected, current levels are within EPA limits. An activated carbon filter can further reduce exposure.
How does Duncan's water compare to other cities?
Duncan ranks #209 out of 358 cities in Oklahoma (better than 42% of state cities) and #13028 out of 15744 cities nationally (17th percentile). The grade of D+ reflects the combined assessment of violation history, lead and copper levels, PFAS contamination, and regulatory compliance.