Water Quality Report · Updated May 12, 2026
CITY OF SAN MARCOS
CITY OF SAN MARCOS delivers tap water graded C (67/100) by TapWaterSafety.org. The utility serves approximately 72,970 residents in SAN MARCOS, Texas using surface water. The most significant water quality concerns are: Perfluorohexane sulfonate (PFHXS) significantly above health guideline; Haloacetic acids (HAA9) significantly above health guideline; Total trihalomethanes (TTHMs) significantly above health guideline. For questions, the utility can be reached at 512-393-8107.
Is SAN MARCOS tap water safe to drink?
CITY OF SAN MARCOS delivers tap water that earns a grade of C (67/100) from TapWaterSafety.org — an average rating, with several contaminants above health guidelines but generally compliant with US legal limits.
The utility serves 72,970 residents in SAN MARCOS, drawing from surface water.
Public testing data identifies 16 contaminants in this water above EWG's health-based guidelines, including: Perfluorohexane sulfonate (PFHXS), Haloacetic acids (HAA9), Total trihalomethanes (TTHMs), Bromochloroacetic acid, Dibromoacetic acid, Bromodichloromethane, Dibromochloromethane, Haloacetic acids (HAA5), Dichloroacetic acid, Bromoform, Trichloroacetic acid, Nitrate, Chloroform, Chlorite, Chromium (hexavalent), Radium, combined (-226 and -228). For most residents, a properly certified home filter at the kitchen tap is the most cost-effective way to reduce exposure to whatever's in your water. See our filter recommendations below, matched specifically to this utility's contaminant profile.
Quick actions for SAN MARCOS residents
Top concerns in this water
Based on the most recent EPA and EWG data, these are the most significant water quality issues for CITY OF SAN MARCOS.
Perfluorohexane sulfonate (PFHXS) significantly above health guideline
Moderate concernPerfluorohexane sulfonate (PFHXS) detected at 0.362 ppt, 362x above the EWG health guideline of 0.001 ppt.
Haloacetic acids (HAA9) significantly above health guideline
Moderate concernHaloacetic acids (HAA9) detected at 19.4 ppb, 323x above the EWG health guideline of 0.06 ppb.
Total trihalomethanes (TTHMs) significantly above health guideline
Moderate concernTotal trihalomethanes (TTHMs) detected at 35.9 ppb, 239x above the EWG health guideline of 0.15 ppb.
Contact CITY OF SAN MARCOS
Reach the utility directly for service issues, water quality concerns, or to request your Consumer Confidence Report.
General Contact
Treatment Plant
Recommended water filters for SAN MARCOS
Filters matched to the specific contaminants in this water supply.
Carbon block (NSF/ANSI 42 + 53)
$40-$750Activated carbon is highly effective for disinfection byproducts like TTHM and HAA5.
Disclosure: TapWaterSafety earns a commission from purchases made through these links. This does not influence our scoring methodology or filter selection.
Score breakdown
This utility's overall score of 67/100 breaks down across five weighted components. Read the full methodology →
Contaminants detected — international standards comparison
Every contaminant detected, compared side-by-side against US EPA legal limits, the EU Drinking Water Directive (2020/2184), WHO Guidelines, and California's Public Health Goal (the strictest US benchmark). Why we show multiple standards →
| Contaminant | Detected | EWG US health-based |
EPA US legal |
EU DWD Europe |
WHO global |
CA PHG strictest US |
Tested sample year |
Status |
|---|---|---|---|---|---|---|---|---|
| Perfluorohexane sulfonate (PFHXS) PFAS |
0.362 ppt | 0.001 | 10.0 | — | — | — | — | 362× over |
| Haloacetic acids (HAA9) Disinfection byproduct |
19.4 ppb | 0.06 | — | — | — | — | — | 323× over |
| Total trihalomethanes (TTHMs) Disinfection byproduct |
35.9 ppb | 0.15 | 80.0 | 100 | — | — | — | 239× over |
| Bromochloroacetic acid Disinfection byproduct |
4.14 ppb | 0.02 | — | — | — | — | — | 207× over |
| Dibromoacetic acid Disinfection byproduct |
5.06 ppb | 0.03 | — | — | — | — | — | 169× over |
| Bromodichloromethane Disinfection byproduct |
8.37 ppb | 0.06 | — | — | — | — | — | 140× over |
| Dibromochloromethane Disinfection byproduct |
13.8 ppb | 0.1 | — | — | — | — | — | 138× over |
| Haloacetic acids (HAA5) Disinfection byproduct |
10.1 ppb | 0.1 | 60.0 | 60 | — | — | — | 101× over |
| Dichloroacetic acid Disinfection byproduct |
3.61 ppb | 0.2 | — | — | — | — | — | 18× over |
| Bromoform Disinfection byproduct |
6.29 ppb | 0.5 | — | — | — | — | — | 13× over |
| Trichloroacetic acid Disinfection byproduct |
1.34 ppb | 0.1 | — | — | — | — | — | 13× over |
| Nitrate Inorganic |
1.69 ppm | 0.14 | 10.0 | 11.3 | 11.3 | 10 | — | 12× over |
| Chloroform Disinfection byproduct |
4.37 ppb | 0.4 | — | — | — | — | — | 11× over |
| Chlorite Disinfection byproduct |
275.1 ppb | 50.0 | 1000.0 | — | — | — | — | 5.5× over |
| Chromium (hexavalent) Heavy metal |
0.0782 ppb | 0.02 | — | — | — | — | — | 3.9× over |
| Radium, combined (-226 and -228) Radiological |
0.17 pCi/L | 0.05 | 5.0 | — | — | — | — | 3.3× over |
| Chlorate Disinfection byproduct |
108.4 ppb | 210.0 | — | — | — | — | — | Below guideline |
| Vanadium Other |
2.28 ppb | 21.0 | — | — | — | — | — | Below guideline |
| Atrazine Pesticide/Herbicide |
0.00667 ppb | 0.1 | 3.0 | 0.1 | 100 | 0.15 | — | Below guideline |
| Barium Heavy metal |
44.4 ppb | 700.0 | 2000.0 | — | 1300 | 2000 | — | Below guideline |
| Aluminum Heavy metal |
35.8 ppb | 600.0 | — | 200 | — | 600 | — | Below guideline |
| Selenium Heavy metal |
0.3 ppb | 30.0 | 50.0 | 20 | 40 | 30 | — | Below guideline |
| Molybdenum Other |
0.185 ppb | 40.0 | — | — | — | — | — | Below guideline |
| Monobromoacetic acid Disinfection byproduct |
0.0333 ppb | 25.0 | — | — | — | — | — | Below guideline |
| Manganese Heavy metal |
0.111 ppb | 100.0 | — | 50 | 80 | — | — | Below guideline |
| Perfluoropentanoic Acid (PFPeA) PFAS |
0.892 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| Monochloroacetic acid Disinfection byproduct |
0.0469 ppb | 53.0 | — | — | — | — | — | Below guideline |
| Perfluorobutanoic Acid (PFBA) PFAS |
0.777 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| Strontium Radiological |
0.541 ppb | 1500.0 | — | — | — | — | — | Below guideline |
| Fluoride Inorganic |
0.197 ppm | — | 4.0 | 1.5 | 1.5 | — | — | Below guideline |
| Hexadecanoic acid Other |
4.87 ppb | — | — | — | — | — | — | Below guideline |
| Lithium Other |
2.02 ppb | — | — | — | — | — | — | Below guideline |
| Octadecanoic acid Other |
5.38 ppb | — | — | — | — | — | — | Below guideline |
All values in the unit of the detected level. Red cells indicate the detected level exceeds that standard. Some contaminants have limits in some jurisdictions but not others (shown as —). The "Tested" column shows the year each contaminant sample was collected.
Sources: US EPA, EU Drinking Water Directive 2020/2184, WHO Guidelines (4th ed.), California OEHHA PHGs, EWG Tap Water Database.
CITY OF SAN MARCOS service area
This water system serves 1 community in Hays County, Texas. Click any city for its dedicated tap water quality page.
Find the right filter for SAN MARCOS water
Browse filter categories by water-quality concern. Each option below is NSF-certified for the matched contaminant type.