Water Quality in Sioux City, IA: 9 Violations — Grade C
Grade C · Score 66/100 · 2 water systems · Updated 2026-05-03
Sioux City'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
EPA monitoring has flagged 9 reportable events for water systems in Sioux City, IA.
Water Quality Map: Sioux City, IA
Each dot represents a ZIP code. Color indicates water quality grade. Tap a dot for details.
Water Quality by ZIP Code in Sioux City
Water quality varies across Sioux City's 9 ZIP codes. Check your specific ZIP for detailed contaminant data.
| ZIP Code | Grade | Score | Violations | Health | |
|---|---|---|---|---|---|
| 51103 | C | 60 | 1 | 0 | View report → |
| 51104 | C | 60 | 1 | 0 | View report → |
| 51106 | C | 65 | 1 | 0 | View report → |
| 51109 | C | 65 | 1 | 0 | View report → |
| 51111 | C | 66 | 1 | 0 | View report → |
| 51101 | B | 70 | 1 | 0 | View report → |
| 51102 | B | 70 | 1 | 0 | View report → |
| 51105 | B | 70 | 1 | 0 | View report → |
| 51108 | B | 70 | 1 | 0 | View report → |
Water Quality Overview
Sioux City, Iowa receives a water quality grade of C with an overall score of 66 out of 100, based on EPA compliance data from the Safe Drinking Water Information System (SDWIS).
The 2 water systems serving Sioux City have accumulated 9 EPA violations (all monitoring/reporting type). These violations are tracked across 9 ZIP codes serving approximately 85,824 people.
What Grade C Means
A grade of C indicates moderate compliance issues. Sioux City'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
The average 90th percentile lead level across Sioux City water systems is 0.0020 mg/L — within EPA limits. No ZIP codes exceed the EPA lead action level.
With 84% of homes built before 1986, Sioux City 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.
Radon Risk
Sioux City is in EPA Radon Zone 1 (High risk). The EPA recommends all homes in Zone 1 areas be tested for radon. Radon is the second leading cause of lung cancer after smoking.
Water Systems Serving Sioux City
Sioux City is served by 2 community water systems regulated under the Safe Drinking Water Act. These systems collectively serve approximately 85,824 people across 9 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 36 enforcement actions against water systems serving Sioux City. Enforcement actions range from informal compliance assistance to formal orders and penalties.
How to Check Your Water in Sioux City
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 Sioux City Water Systems
The following contaminants have been detected or caused violations across Sioux City's water systems:
| Contaminant | Category | MCL | Violations | ZIPs Affected | Health-Based |
|---|---|---|---|---|---|
| Haloacetic Acids (HAA5) | Disinfection Byproducts | 0.06 mg/L | 9 | 9 | No |
MCL = Maximum Contaminant Level (EPA enforceable standard). Health-based violations indicate levels that may pose direct health risks.
EPA Enforcement History
The EPA and state regulators have taken 4 enforcement actions against water systems serving Sioux City. Recent actions:
| Date | Action Type |
|---|---|
| 2025-05-12 | State Informal Action |
| 2024-08-13 | State Order Extension |
| 2024-07-17 | State Informal Enforcement |
| 2024-07-17 | State Filed Judgment |
Enforcement actions range from informal compliance assistance to formal orders and penalties. The most recent action was on 2025-05-12.
Sioux City vs. Nearby Iowa Cities
How Sioux City's water quality compares to similar cities in Iowa:
| City | Grade | Violations | Systems | Population |
|---|---|---|---|---|
| Sioux City | C | 9 | 2 | 85,824 |
| Ankeny | C | 8 | 5 | 80,314 |
| Ames | C | 10 | 5 | 97,632 |
| Iowa City | D | 84 | 5 | 98,352 |
Water Quality by ZIP Code in Sioux City
Water quality varies across Sioux City's ZIP codes. The table below shows the worst-scoring and best-scoring areas:
| ZIP Code | Score | Grade | Violations | Health-Based |
|---|---|---|---|---|
| 51103 | 60 | C | 1 | 0 |
| 51104 | 60 | C | 1 | 0 |
| 51106 | 65 | C | 1 | 0 |
| 51109 | 65 | C | 1 | 0 |
| 51111 | 66 | C | 1 | 0 |
| 51101 | 70 | B | 1 | 0 |
| 51102 | 70 | B | 1 | 0 |
| 51105 | 70 | B | 1 | 0 |
| 51108 | 70 | B | 1 | 0 |
Common Questions About Sioux City Water
These are the most common questions residents search for about water quality in Sioux City, Iowa:
Is Sioux City water hard or soft? Water hardness varies by source. Sioux City's 2 water systems use multiple sources. Check your ZIP code report for specific hardness data.
Can I drink Sioux City tap water? Sioux City's water receives a grade of C (66/100). No health-based violations have been recorded, but home testing is always recommended.
What is the best water filter for Sioux City? A NSF/ANSI 53-certified filter for lead removal is a good general choice. See our Water Filter Matcher for personalized recommendations.
Sioux City vs. Iowa Average
Understanding how Sioux City compares to the broader Iowa 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 Sioux City.
ZIP Codes in Sioux City
Sioux City spans 9 ZIP codes. The ZIP with the lowest water quality score is 51101. 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.