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Public water system record

City of San Marcos

Serves San Marcos, Hays County, TX · 72,970 people served

Federal records show 1 health-based violation and 1 monitoring/reporting issue for City of San Marcos in the last ten years. The most serious issue in this window was a Total Trihalomethanes (TTHMs) violation that EPA lists as archived, not resolved.

  • TX1050001
  • SAN MARCOS
  • TX
  • 72,970 served

System profile

Source water Surface water
ZIP 78666
EPA system ID TX1050001

Verify this system on EPA ECHO →

Health-based violations, last 10 years
1
Resolved
0
Unresolved
0
Archived by EPA
1
Any acute record
No
Monitoring issues, last 10 years
1

Key facts

  • City of San Marcos draws water from 8 wells and 1 surface water intake.
  • Highest measured level in the last 10 years: Total Trihalomethanes (TTHMs), 0.081 mg/L, federal limit 0.08 mg/L (at or just above the limit), 2025.
  • Most recent formal enforcement: compliance order with a penalty by Texas, April 2015.
  • Record on file since 2003, with 6 health-based violations before October 19, 2016.
  • Lead pipe inventory: 0 lead and 3,146 unknown out of 17,681 service lines.

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Health-based violations

Since October 2016

Violation data reflects EPA records through March 2026. For the most current status, visit the EPA ECHO database.

Contaminant Rule family Start date Status Acute
Total Trihalomethanes (TTHMs)
Contaminant limit exceeded
Measured 0.081 mg/L, federal limit 0.08 mg/L (at or just above the limit)
 220 Oct 1, 2025 Archived
Violation period ended. EPA no longer counts it toward current compliance, but no fix was formally recorded.
 No

Monitoring and reporting issues

Since October 2016

Missed tests or reports, not contaminants found above a limit.

Issue Start date Status
Chlorite
Monitoring and reporting
 Feb 1, 2021 Resolved

Full record since 2003

EPA's records for City of San Marcos go back to 2003. Before October 19, 2016 they list 6 health-based violations (6 resolved) and 3 monitoring or reporting violations.

Violations that began in Health-based Monitoring and reporting
2000s 1 0
2010 to October 18, 2016 5 3
2020s 1 1

Most recent health-based violation before October 19, 2016: Total Trihalomethanes (TTHMs), began January 2016, Resolved.

Show all 6 health-based violations before October 19, 2016
Contaminant Start date Status
Total Trihalomethanes (TTHMs)
Contaminant limit exceeded
Measured 0.082 mg/L, federal limit 0.08 mg/L (at or just above the limit)
 Jan 1, 2016 Resolved
Total Trihalomethanes (TTHMs)
Contaminant limit exceeded
Measured 0.086 mg/L, federal limit 0.08 mg/L (1.1 times the limit)
 Jul 1, 2014 Resolved
Total Trihalomethanes (TTHMs)
Contaminant limit exceeded
Measured 0.081 mg/L, federal limit 0.08 mg/L (at or just above the limit)
 Apr 1, 2014 Resolved
Total Trihalomethanes (TTHMs)
Contaminant limit exceeded
Measured 0.086 mg/L, federal limit 0.08 mg/L (1.1 times the limit)
 Jan 1, 2014 Resolved
Total Trihalomethanes (TTHMs)
Contaminant limit exceeded
Measured 0.087 mg/L, federal limit 0.08 mg/L (1.1 times the limit)
 Oct 1, 2013 Resolved
Surface Water Treatment Rule
Treatment technique failure
 Jan 1, 2003 Resolved

Enforcement actions

Texas regulators took 1 formal enforcement action against City of San Marcos in 2015. The most recent was a compliance order with a penalty in April 2015.

Date By Action Violations covered
Apr 9, 2015 Texas Compliance order with a penalty 4 violations (4 health-based): Total Trihalomethanes (TTHMs)

What the violations mean

Total Trihalomethanes (TTHMs)

1 incident

Disinfection byproduct levels exceeded the federal limit

Long-term TTHM exposure may increase bladder cancer risk

Where the water comes from

City of San Marcos draws water from 8 wells and 1 surface water intake. It also buys water from Alliance Regional Water Authority 1B. 1 other community water system buys water from City of San Marcos. 2 other public water systems have emergency connections to City of San Marcos.

Buys water from

Community systems that buy water from it

Annual water quality report

City of San Marcos must give its customers an annual water quality report (Consumer Confidence Report) by July 1, with the levels its tests found in the previous year.

Systems serving 10,000 or more people must mail or deliver the report to every customer, and from 2027 they must send it twice a year.

Find a posted report with EPA's Consumer Confidence Report search

Testing your own water

To test the water at your tap, or a private well this record does not cover, use a laboratory certified for drinking water by Texas.

Certified drinking water labs by state EPA guidance for private wells