Tap Water Quality Report
Tap water quality in SAN MARCOS, Texas
Tap water in SAN MARCOS, Texas receives a grade of D (67/100) from TapWaterSafety.org. It's served by CITY OF SAN MARCOS. 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. Data sources: EPA SDWIS, EPA ECHO, EWG Tap Water Database.
What's in SAN MARCOS's tap water
Top water quality concerns identified by the EPA and Environmental Working Group across the utility serving 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.
Recommended filters for SAN MARCOS
Filters matched to the specific contaminants in SAN MARCOS's 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.
All contaminants detected in SAN MARCOS's tap water
Every contaminant identified, compared side-by-side against US EPA legal limits, the EU Drinking Water Directive (2020/2184), WHO Guidelines, and California's Public Health Goal. 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, California OEHHA PHGs, EWG Tap Water Database.
Treatment plant contact info
For service issues, water quality concerns, or to request a Consumer Confidence Report from CITY OF SAN MARCOS.