Is Seneca, IL 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 ↓
92.7/100
waterverge.com Seneca, IL — Water Quality Report
Seneca's drinking water received a grade of A (92.7 out of 100), indicating excellent water quality. The city's 1 water system serves approximately 2,353 residents using groundwater.
Lead levels were measured at 0.0 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 19 violations on record, including 10 health-based violations. 1 remains unresolved.
What to know about Seneca's water
Seneca ranks #59 out of 891 cities in Illinois for water quality, placing it one of the best in the state.
Seneca 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.
As a small community water system, Seneca may have fewer resources for advanced treatment technologies and infrastructure upgrades compared to larger utilities.
Water quality score
See methodology →Is Seneca, IL water safe to drink?
Seneca's tap water meets most EPA standards but has areas that warrant attention. With a grade of A (92.7/100), some contaminant levels or compliance issues suggest that residents may benefit from additional filtration. The city's 1 water system serves approximately 2,353 residents using groundwater (wells).
Recent water quality updates for Seneca
A timeline of significant water quality events, violations, and data updates.
Latest EPA compliance and testing data incorporated into Seneca's water quality assessment. Grade: A (92.7/100).
Contaminants: TTHM, Total Haloacetic Acids (HAA5).
1 health-based. Contaminants: Combined Radium (-226 and -228).
1 health-based. Contaminants: Combined Radium (-226 and -228).
Key contaminant findings
Based on the most recent EPA sampling data for Seneca's water supply.
Well within EPA limits.
Violation history
Seneca's water system has 19 total violations on record, including 10 health-based violations. 1 remain unresolved.
Where does Seneca's water come from?
Seneca's drinking water comes from groundwater (wells), supplied by 1 water system serving approximately 2,353 people. Groundwater is generally less susceptible to surface contamination but can contain naturally occurring contaminants like arsenic, radon, and nitrate. Nearby water bodies include Illinois River (river), Hanson Gravel Pit (river).
What Seneca 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.
Data: EPA SDWIS, UCMR 5 (PFAS), FEMA, NOAA. Last updated May 2026.
Top contaminants to know
View all ↓Violation summary
Violations & advisories
Top industrial polluters within 10 miles of Seneca
Industrial polluters nearby
Reported releases to surface water by facilities near Seneca, ranked by pounds discharged annually.
Total reported releases to surface water: 21 lbs
| Facility | Top chemical | To surface water (lbs/yr) | Distance |
|---|---|---|---|
SABIC INNOVATIVE PLASTICS US LLC OTTAWA, IL61350 | Chromium and Chromium Compounds(except for chromite ore mined in the Transvaal Region) | 16 | 7.3 mi |
REG SENECA LLC SENECA, IL61360 | Methanol | 5 | 1.0 mi |
H.B. FULLER CO MORRIS, IL60450 | — | — | 2.9 mi |
OLDCASTLE LAWN & GARDEN MARSEILLES, IL61341 | — | — | 3.9 mi |
PCS PHOSPHATE MARSEILLES MARSEILLES, IL61341 | — | — | 1.5 mi |
Source: EPA Toxic Release Inventory (TRI) 2023
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 |
Lead level trend (90th percentile)
See how Seneca compares by contaminant
Explore where Seneca ranks among all Illinois cities for specific contaminants.
Water source & infrastructure
Where Seneca's water comes from
Seneca'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 local government ownership and serves approximately 2,353 people through 1 water system.
Water bodies near Seneca
Seneca is located near 2 notable water bodies. These water bodies contribute to the regional watershed and may indirectly affect groundwater quality.
Water systems serving Seneca
| System Name | PWSID | Population | Source |
|---|---|---|---|
| SENECA | IL0991050 | 2,353 | GW |
How Seneca compares
Full Illinois rankings →Seneca's score of 92.7/100 is above the average of 56/100 among major Illinois cities. It outscores 10 of 10 nearby cities.
Nearby cities
View Illinois rankings →About Seneca, IL
Learn more about your water
Guides and resources related to Seneca's water quality findings.
Explore water quality across Lasalle
Frequently asked questions
Is Seneca, IL tap water safe to drink?
Seneca's water quality earned a grade of A (92.7/100). The water generally meets EPA standards and is considered safe for consumption. The city ranks #59 out of 891 cities tested in Illinois.
What contaminants are in Seneca's water?
Lead was measured at 0.0 ppb (90th percentile). 19 violations are on record.
How is Seneca'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 Seneca?
Based on current data, basic filtration should suffice for additional peace of mind.
Where does Seneca's water come from?
Seneca's water is sourced from Groundwater. The city has 1 water system serving approximately 2,353 residents.
What health violations has Seneca's water system had?
Seneca has 10 health-based violations on record. The most recent violation was recorded in September 2015. Health-based violations mean the water exceeded EPA maximum contaminant levels (MCLs) for a regulated substance. 1 violation remains unresolved.
Is Seneca's groundwater at risk of contamination?
Seneca 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 19 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 Seneca's water compare to other cities?
Seneca ranks #59 out of 891 cities in Illinois (better than 93% of state cities) and #1137 out of 15744 cities nationally (93th percentile). The grade of A reflects the combined assessment of violation history, lead and copper levels, PFAS contamination, and regulatory compliance.
Does Seneca's small water system affect quality?
Seneca's system serves approximately 2,353 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 19 violations on record.