Is Thomas, OK Tap Water Safe to Drink?
Graded A+, with 1 unresolved violation on record. See what was cited — and what it means for your tap. What to do next ↓
96.3/100
waterverge.com Thomas, OK — Water Quality Report
Thomas's drinking water received a grade of A+ (96.3 out of 100), indicating excellent water quality. The city's 1 water system serves approximately 1,238 residents using groundwater.
Lead levels were measured at 2.5 ppb (90th percentile), well within EPA limits. This system has not yet been tested for PFAS under the EPA UCMR 5 program.
The system has 27 violations on record, including 0 health-based violations. 1 remains unresolved.
What to know about Thomas's water
Thomas ranks #1 out of 358 cities in Oklahoma for water quality, placing it one of the best in the state.
Thomas relies on groundwater, which is generally less vulnerable to surface contamination but can be affected by naturally occurring minerals like arsenic and nitrate, as well as agricultural and industrial runoff.
Hexavalent chromium (chromium-6) was detected at 2.80 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.
As a small community water system, Thomas may have fewer resources for advanced treatment technologies and infrastructure upgrades compared to larger utilities.
Water quality score
See methodology →Is Thomas, OK water safe to drink?
Thomas's tap water meets most EPA standards but has areas that warrant attention. With a grade of A+ (96.3/100), some contaminant levels or compliance issues suggest that residents may benefit from additional filtration. The city's 1 water system serves approximately 1,238 residents using groundwater (wells).
Recent water quality updates for Thomas
A timeline of significant water quality events, violations, and data updates.
Latest EPA compliance and testing data incorporated into Thomas's water quality assessment. Grade: A+ (96.3/100).
Contaminants: Revised Total Coliform Rule.
Contaminants: Coliform (TCR).
Contaminants: Coliform (TCR).
Federal disaster declaration (FEMA DR-3219). Hurricane event — may have impacted local water infrastructure.
Federal disaster declaration (FEMA DR-794). Flood event — may have impacted local water infrastructure.
Key contaminant findings
Based on the most recent EPA sampling data for Thomas's water supply.
Well within EPA limits.
Violation history
Thomas's water system has 27 total violations on record, including 0 health-based violations. 1 remain unresolved.
Flood & environmental risk
Custer County has experienced 4 federally declared disasters since 1982. Flooding and severe storms can overwhelm water treatment plants, cause sewage overflows, and introduce agricultural runoff, bacteria, and sediment into drinking water supplies.
Where does Thomas's water come from?
Thomas's drinking water comes from groundwater (wells), supplied by 1 water system serving approximately 1,238 people. Groundwater is generally less susceptible to surface contamination but can contain naturally occurring contaminants like arsenic, radon, and nitrate.
What Thomas 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.
Thomas'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 ↓Violation summary
Violations & advisories
Drought conditions
D3 — extreme droughtCuster County is currently in D3 (extreme 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
Custer County has experienced 4 federally declared disasters since 1982. Flooding and severe weather can compromise water treatment infrastructure and introduce contaminants into drinking water supplies.
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. | 2.5 | 15 | ppb | Inorganic | Safe |
Lead level trend (90th percentile)
See how Thomas compares by contaminant
Explore where Thomas ranks among all Oklahoma cities for specific contaminants.
Water source & infrastructure
Where Thomas's water comes from
Thomas's drinking water is drawn from underground aquifers through wells.
Groundwater is naturally filtered through rock and soil layers, generally requiring less treatment than surface water. However, it can contain naturally occurring contaminants like arsenic, radon, and minerals.
Agricultural activity, septic systems, and industrial operations near well fields can introduce nitrates, pesticides, and volatile organic compounds.
The system is operated by private ownership and serves approximately 1,238 people through 1 water system.
Water systems serving Thomas
| System Name | PWSID | Population | Source |
|---|---|---|---|
| THOMAS | OK2002001 | 1,238 | GW |
How Thomas compares
Full Oklahoma rankings →Thomas's score of 96.3/100 is above the average of 45/100 among major Oklahoma cities. It outscores 10 of 10 nearby cities.
Nearby cities
View Oklahoma rankings →About Thomas, OK
Learn more about your water
Guides and resources related to Thomas's water quality findings.
Explore water quality across Custer
Frequently asked questions
Is Thomas, OK tap water safe to drink?
Thomas's water quality earned a grade of A+ (96.3/100). The water generally meets EPA standards and is considered safe for consumption. The city ranks #1 out of 358 cities tested in Oklahoma.
What contaminants are in Thomas's water?
Lead was measured at 2.5 ppb (90th percentile). 27 violations are on record.
How is Thomas'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 Thomas?
Based on current data, basic filtration should suffice for additional peace of mind.
Where does Thomas's water come from?
Thomas's water is sourced from Groundwater. The city has 1 water system serving approximately 1,238 residents.
Is Thomas's groundwater at risk of contamination?
Thomas uses groundwater, which can be affected by naturally occurring contaminants like arsenic, radon, and nitrate, as well as agricultural runoff and industrial activity. The system has 27 violations on record that may relate to groundwater quality. Groundwater systems are generally less susceptible to surface contamination but should be monitored for emerging contaminants like PFAS.
How does Thomas's water compare to other cities?
Thomas ranks #1 out of 358 cities in Oklahoma (better than 100% of state cities) and #198 out of 15744 cities nationally (99th percentile). The grade of A+ reflects the combined assessment of violation history, lead and copper levels, PFAS contamination, and regulatory compliance.
Does Thomas's small water system affect quality?
Thomas's system serves approximately 1,238 residents. Small community water systems (under 3,300 people) may have fewer financial resources for infrastructure upgrades and advanced treatment technologies. However, they are held to the same EPA drinking water standards as larger systems. This system has 27 violations on record.