San Luis Obispo County Water Quality…
37 water systems · 20 ZIP codes · Average ZIP-level Home Safety model score 77/100 (B) · 14 of 34 tracked ZIP records scored
Data: EPA Safe Drinking Water Information System (SDWIS), EPA ECHO
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Find the Right Filter →Water Quality Overview
San Luis Obispo County has 37 community water systems across 20 directly mapped ZIP records. The systems report serving approximately 252,617 people. The available records contain 57 EPA violations, including 31 health-based violations.
Health-based violations account for 54% of all violations in San Luis Obispo County. These violations indicate contaminant levels that may pose direct risks to human health.
Year-by-year violation counts, enforcement actions and violation counts by contaminant are not shown for this county: the source records them per ZIP code, so a water system serving several ZIP codes would be counted several times. The county totals above count each water system once.
Violation Breakdown
| Violation Type | Count | Percentage |
|---|---|---|
| Health-based | 31 | 54.4% |
| Monitoring/Reporting | 26 | 45.6% |
| Total | 57 | 100% |
Health-based violations are MCL, MRDL (disinfectant) and treatment-technique violations. Monitoring violations indicate failures to test or report.
Cities with Most Violations
| Rank | City | Violations | Health-Based | ZIP Codes | Population |
|---|---|---|---|---|---|
| 1 | Arroyo Grande | 37 | 13 | 1 | 32,016 |
| 2 | Oceano | 37 | 13 | 1 | 6,812 |
| 3 | Nipomo | 13 | 12 | 1 | 21,495 |
| 4 | Paso Robles | 12 | 12 | 1 | 45,859 |
| 5 | Pismo Beach | 4 | 3 | 1 | 8,024 |
| 6 | San Luis Obispo | 2 | 1 | 5 | 63,924 |
| 7 | Morro Bay | 1 | 1 | 1 | 11,336 |
| 8 | Cambria | 1 | 1 | 1 | 6,269 |
Most Common Contaminants
| Contaminant | Category | ZIPs Affected | Health-Based |
|---|---|---|---|
| Nitrate | Inorganic | 5 | Yes |
| Haloacetic Acids (HAA5) | Disinfection Byproducts | 2 | Yes |
| Lead and Copper Rule Revisions | Treatment Technique | 2 | Yes |
| Lead and Copper Rule | Treatment Technique | 3 | No |
| Surface Water Treatment Rule | Treatment Technique | 2 | Yes |
| Fluoride | Inorganic | 1 | Yes |
| Total Trihalomethanes (TTHM) | Disinfection Byproducts | 1 | Yes |
Water Data and the Home Safety Score
This page reports EPA water-system facts without converting the broader Home Safety Score into a drinking-water grade. The county Home Safety grade (B) is a separate multi-source index that also requires PFAS screening, radon, and annual air-quality evidence. Check each ZIP report for the versioned score and its component coverage.
Water Systems in San Luis Obispo County
San Luis Obispo County is served by 37 community water systems, averaging 1.1 systems per ZIP code. Each system is independently regulated and tested by the EPA. Larger systems serving more people typically have more extensive monitoring requirements.
Water systems in San Luis Obispo County source water from a mix of surface water (rivers, reservoirs) and groundwater (wells, aquifers). Source type affects which contaminants are most likely to be detected.
How to Check Your Water in San Luis Obispo County
Enter your ZIP code on ZipCheckup for detailed water-system data including contaminant levels and violation history; the Home Safety Score is shown separately with its model version
Request your CCR — every water utility must provide an annual Consumer Confidence Report
Get a home test — certified kits ($20-$50) or professional lab tests ($150-$400) can detect contaminants not covered by routine testing
Consider filtration — NSF-certified filters can address specific contaminants found in your area
Check for lead — homes built before 1986 should test for lead regardless of utility compliance
Data Sources
- Water quality: EPA Safe Drinking Water Information System (SDWIS)
- Enforcement: EPA ECHO
Source publication schedules vary. See the page source and verification fields for available timing evidence.
Water Quality by ZIP Code in San Luis Obispo County
Water quality varies across San Luis Obispo County's 20 ZIP codes. Each row counts the EPA violations of every water system mapped to that ZIP, so a system serving several ZIP codes appears in several rows and the rows do not add up to the county total. Check your specific ZIP for detailed contaminant data.
| ZIP Code | City | Violations | Health | |
|---|---|---|---|---|
| 93445 | Oceano | 37 | 13 | View → |
| 93420 | Arroyo Grande | 37 | 13 | View → |
| 93444 | Nipomo | 13 | 12 | View → |
| 93446 | Paso Robles | 12 | 12 | View → |
| 93449 | Pismo Beach | 4 | 3 | View → |
| 93401 | San Luis Obispo | 1 | 1 | View → |
| 93409 | San Luis Obispo | 1 | 0 | View → |
| 93428 | Cambria | 1 | 1 | View → |
| 93442 | Morro Bay | 1 | 1 | View → |
| 93405 | San Luis Obispo | 0 | 0 | View → |
| 93433 | Grover Beach | 0 | 0 | View → |
| 93465 | Templeton | 0 | 0 | View → |
| 93402 | Los Osos | 0 | 0 | View → |
| 93422 | Atascadero | 0 | 0 | View → |
| 93407 | San Luis Obispo | 0 | 0 | View → |
| 93410 | San Luis Obispo | 0 | 0 | View → |
| 93424 | Avila Beach | 0 | 0 | View → |
| 93430 | Cayucos | 0 | 0 | View → |
| 93432 | Creston | 0 | 0 | View → |
| 93453 | Santa Margarita | 0 | 0 | View → |
What are EPA health violations?
Health-based violations are EPA violations of a Maximum Contaminant Level (MCL), a Maximum Residual Disinfectant Level (MRDL) or a required treatment technique - the enforceable standards designed to protect human health. San Luis Obispo County has 31 such violations. Not all violations cause illness; review each violation type and duration to understand possible health implications.
Water facts and the Home Safety Score
The score shown here is the broader Home Safety Score, not a water-quality grade. Model 4.0.0 combines EPA SDWIS identity plus accepted ECHO SDWA lifecycle-based water compliance, PFAS screening, radon zones, and annual air-quality evidence. San Luis Obispo County has a score of 77/100 (Grade B) across 14 scored of 34 tracked ZIP records.
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Find the Right Filter →Frequently Asked Questions
Is the tap water safe in San Luis Obispo County, California?
San Luis Obispo County has 37 community water systems with 57 recorded EPA violations, including 31 health-based. Water quality varies by ZIP code - check your specific location for detailed results.
How many water violations does San Luis Obispo County have?
The 37 water systems with EPA records that serve ZIP codes in San Luis Obispo County have 57 recorded EPA violations, each system counted once. 31 are health-based.
Which city in San Luis Obispo County has the most water violations?
Arroyo Grande has the most violations in San Luis Obispo County with 37 recorded EPA violations for the 9 water systems serving its 1 ZIP code.
What contaminants are found in San Luis Obispo County water?
San Luis Obispo County water systems are monitored for over 90 EPA-regulated contaminants including lead, copper, nitrates, disinfection byproducts, and bacteria. Check your ZIP code for contaminant-specific data.
How can I test my water in San Luis Obispo County?
Contact your local water utility for free or low-cost testing. You can also use a certified home test kit ($20-$50) or hire a certified lab ($150-$400).