Water Quality in San Marcos, TX: 45 Violations Recorded for Mapped Water Systems
5 water systems · 1 directly mapped ZIP records
Available EPA records report 45 violations across 1 directly mapped ZIP records with known counts for San Marcos. This is compliance evidence, not a property-level tap-water verdict.
Data: EPA Safe Drinking Water Information System (SDWIS)
Water Quality by ZIP Code in San Marcos
This table shows typed EPA water evidence only. Missing violation counts are displayed as N/A, not zero.
| ZIP Code | Violations | Health | |
|---|---|---|---|
| 78666 | 45 | 21 | View report → |
Violation Trend
EPA violations recorded for water systems serving San Marcos.
| Year | Total violations | Health-based |
|---|---|---|
| 2021 | 2 | 2 |
| 2022 | 4 | 4 |
| 2023 | 4 | 4 |
| 2024 | 4 | 4 |
| 2025 | 3 | 3 |
Water Quality Overview
San Marcos, Texas has directly mapped EPA water-system data for 1 ZIP codes. This page reports typed compliance facts and does not relabel the multi-source Home Safety Score as a drinking-water grade.
The available EPA records report 45 violations, including 21 health-based violations across 1 directly mapped ZIP record with reported counts.
Lead Levels
The average of the reported 90th-percentile lead results across the ZIP codes of San Marcos is 0.0069 mg/L; the EPA action level of 0.015 mg/L applies to a water system's own 90th-percentile result and is not a safety threshold (EPA's health goal for lead is zero). No exceedances appear among the 1 ZIP records with known lead status.
Water Systems Serving San Marcos
San Marcos is served by 5 community water systems regulated under the Safe Drinking Water Act. About 87,775 people live in the area (2 ZIP codes, Census); this is not the systems' reported service population.
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
EPA records list 10 enforcement actions against water systems serving San Marcos. Enforcement actions range from informal compliance assistance to formal orders and penalties.
How to Check Your Water in San Marcos
Enter your ZIP code on ZipCheckup to see your specific water system data, including contaminant levels and violation history
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 San Marcos Water Systems
The following contaminants have been detected or caused violations across San Marcos's water systems:
| Contaminant | Category | MCL | Violations | ZIPs Affected | Health-Based |
|---|---|---|---|---|---|
| Haloacetic Acids (HAA5) | Disinfection Byproducts | 0.06 mg/L | 21 | 1 | Yes |
| Stage 2 DBP Rule | Treatment Technique | N/A | 4 | 1 | Yes |
| Lead and Copper Rule | Treatment Technique | N/A | 4 | 1 | No |
| Surface Water Treatment Rule | Treatment Technique | N/A | 3 | 1 | No |
| Fecal Coliform | Microbiological | N/A | 2 | 1 | No |
| Revised Total Coliform Rule | Microbiological | N/A | 2 | 1 | No |
| Stage 1 DBP Rule | Treatment Technique | N/A | 2 | 1 | No |
| E. coli | Microbiological | N/A | 1 | 1 | No |
| Chlorite | Disinfection Byproducts | 1 mg/L | 1 | 1 | No |
| Total Coliform | Microbiological | N/A | 1 | 1 | No |
The standard column shows the EPA Maximum Contaminant Level (MCL) except for lead and copper, whose value is an action level that triggers corrective steps and is not an MCL. Health-based violations are MCL, MRDL and treatment-technique violations.
Violation Trend Over Time
Year-by-year EPA violations recorded for water systems serving San Marcos:
| Year | Total Violations | Health-Based |
|---|---|---|
| 2021 | 2 | 2 |
| 2022 | 4 | 4 |
| 2023 | 4 | 4 |
| 2024 | 4 | 4 |
| 2025 | 3 | 3 |
Violations have increased from 2 in 2021 to 3 in 2025. This trend warrants monitoring.
EPA Enforcement History
The EPA and state regulators have taken 10 enforcement actions against water systems serving San Marcos. Recent actions:
| Date | Action Type |
|---|---|
| 2026-06-01 | State Informal Action |
| 2026-06-01 | State Informal Enforcement |
| 2026-05-07 | State Informal Action |
| 2026-03-26 | State Informal Action |
| 2026-03-26 | State Order Extension |
| 2026-03-12 | State Order Extension |
| 2026-03-09 | State Informal Action |
| 2026-03-09 | State Informal Enforcement |
| 2026-01-29 | State Order Extension |
| 2025-12-08 | State Informal Action |
Enforcement actions range from informal compliance assistance to formal orders and penalties. The most recent action was on 2026-06-01.
San Marcos vs. Nearby Texas Cities
How San Marcos's water quality compares to similar cities in Texas:
| City | Direct EPA ZIPs | Violations | Systems | Population |
|---|---|---|---|---|
| San Marcos | 1 | 45 | 5 | 87,775 |
| Cedar Park | 1 | 14 | 5 | 89,162 |
| Victoria | 3 | 20 | 3 | 86,300 |
| Weatherford | 4 | 217 | 12 | 83,084 |
Common Questions About San Marcos Water
These are the most common questions residents search for about water quality in San Marcos, Texas:
Is San Marcos water hard or soft? Water hardness varies by source. San Marcos's 5 water systems use multiple sources. Check your ZIP code report for specific hardness data.
Can I drink San Marcos tap water? City-level EPA records cannot determine safety at a specific tap. The measured subset contains 21 health-based violations; check the affected utility record and consider certified testing.
What is the best water filter for San Marcos? A NSF/ANSI 53-certified filter for lead removal is a good general choice. See our Water Filter Matcher for personalized recommendations.
San Marcos vs. Texas Average
Understanding how San Marcos compares to the broader Texas 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 San Marcos.
ZIP Codes in San Marcos
San Marcos spans 2 ZIP codes. EPA water-system coverage is available for 1 directly mapped ZIP code. 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
Source reporting periods vary. See each cited source for its publication schedule.