San Marcos, TX Water Quality Report

Is San Marcos tap water safe? See PFAS and lead contamination levels for San Marcos, Texas. Compare to EPA limits and get filter recommendations.

Quick Answers

Is San Marcos tap water safe to drink? San Marcos tap water meets most federal EPA limits, but PFAS compounds have been detected at an average of 2.99 ppt across 5 compounds. A certified pitcher filter or reverse osmosis system is recommended for sensitive populations.

What contaminants are in San Marcos water? Top PFAS compounds detected in San Marcos water: lithium (11.3 ppt), PFBA (0.01 ppt), PFPeA (0 ppt). See the full table for all monitored contaminants and comparison to EPA limits.

What filter should I use in San Marcos? Reverse osmosis removes 90%+ of PFAS, lead, and arsenic. NSF-53 certified pitcher and faucet filters (ZeroWater, Clearly Filtered, LifeStraw) work for smaller households. Skip standard Brita filters for PFAS removal.

San Marcos Water Quality Summary

EPA testing has detected PFAS "forever chemicals" in San Marcos drinking water. Recent monitoring found a peak level of 11.3 ppt across 4 water systems, representing an average of 2.99 ppt across 5 detected compounds.

Contamination Level: LOW – Low contamination – PFAS detected but at lower levels; monitoring continues.

Top Detected Compounds

  • lithium: 11.3 ppt (exceeds EPA 4 ppt limit for PFOA/PFOS)
  • PFBA: 0.01 ppt
  • PFPeA: 0 ppt
  • PFHxA: 0 ppt
  • PFHxS: 0 ppt

Lead in San Marcos Water

EPA Lead and Copper Rule testing has recorded 22 lead samples for San Marcos water systems, with a 90th-percentile high of 0.0032 mg/L (within the EPA 0.015 mg/L action level). There is no safe level of lead for children; if your home was built before 1986, a certified NSF/ANSI 53 lead-removal filter is recommended.

EPA Violations in San Marcos

San Marcos public water systems have 71 health-based EPA Safe Drinking Water Act violations on record, including Haloacetic Acids (HAA5), Selenium, Arsenic, Total Trihalomethanes (TTHMs), Total Organic Carbon. Health-based violations mean a contaminant exceeded its federal limit or required treatment was not applied.

About the Data

These figures come from the EPA's Unregulated Contaminant Monitoring Rule 5 (UCMR5) testing program, 2023-2025. UCMR5 is the most comprehensive national drinking water survey in US history, covering 66,000+ public water systems. Population of San Marcos: approximately 67,553.

ZIP Codes Served

78666, 78667

What San Marcos Residents Should Do

  1. Enter your exact ZIP code at knowyourexposure.com for address-level data
  2. Install an NSF/ANSI 58 reverse osmosis filter (removes 94-99% of PFAS)
  3. If you're in a high-exposure group (pregnant, young children), consider a PFAS home test kit
  4. Review your utility's Consumer Confidence Report (CCR) annually