What was found in ZIP 78666
The level at this ZIP's main supplier, the highest level anywhere in it, the EPA limit for each, and where the figure comes from.
| Contaminant | Level vs EPA limit | Suppliers | Source |
|---|---|---|---|
| Nitrate-Nitrite | 2172 µg/L 22% of the EPA limit 10000 µg/L Main supplier: CITY OF SAN MARCOS · 72,970 people · 2015 | 3/4 | SYR4 |
| Nitrate | 1990.4999999999998 µg/L 20% of the EPA limit 10000 µg/L Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019
Highest in the ZIP: 2022.4999999999995 µg/L — CRYSTAL CLEAR SUD · 20,766 people · 2019 | 3/4 | SYR4 |
| Copper | 250.49999999999983 µg/L 19% of the EPA limit 1300 µg/L Main supplier: CITY OF SAN MARCOS · 72,970 people · 2018
Highest in the ZIP: 1700 µg/L — TEXAS STATE UNIVERSITY - SAN MARCOS · 43,552 people · 2019 | 4/4 | SYR4 |
| Fluoride | 765 µg/L 19% of the EPA limit 4000 µg/L Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019 | 3/4 | SYR4 |
| Chlorite | 604 µg/L 60% of the EPA limit 1000 µg/L Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019 | 1/4 | SYR4 |
| Nitrite | 115 µg/L 12% of the EPA limit 1000 µg/L Highest in the ZIP: CRYSTAL CLEAR SUD · 20,766 people · 2019 | 1/4 | SYR4 |
| TTHM | 88.075 µg/L 110% of the EPA limit, at the 95th percentile of samples — 80 µg/L Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019
Highest in the ZIP: 113.17999999999994 µg/L — MAXWELL SUD · 16,104 people · 2019 | 4/4 | SYR4 |
| Total Haloacetic Acids (HAA5) | 35.025 µg/L 58% of the EPA limit 60 µg/L Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019
Highest in the ZIP: 58.269999999999584 µg/L — CRYSTAL CLEAR SUD · 20,766 people · 2019 | 4/4 | SYR4 |
| Barium | 46.76 µg/L 2.3% of the EPA limit 2000 µg/L Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019 | 3/4 | SYR4 |
| Chloroform | 27.58499999999998 µg/L No EPA limit set Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019
Highest in the ZIP: 43.71999999999993 µg/L — MAXWELL SUD · 16,104 people · 2019 | 4/4 | SYR4 |
| Bromodichloromethane | 26.279999999999998 µg/L No EPA limit set Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019
Highest in the ZIP: 36.09499999999999 µg/L — MAXWELL SUD · 16,104 people · 2019 | 4/4 | SYR4 |
| Dichloroacetic Acid | 16.94999999999999 µg/L No EPA limit set Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019
Highest in the ZIP: 35.2 µg/L — CRYSTAL CLEAR SUD · 20,766 people · 2019 | 4/4 | SYR4 |
| Dibromochloromethane | 23.95499999999999 µg/L No EPA limit set Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019
Highest in the ZIP: 25.894999999999992 µg/L — MAXWELL SUD · 16,104 people · 2019 | 4/4 | SYR4 |
| Monochloroacetic Acid | 12.319999999999993 µg/L No EPA limit set Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019 | 3/4 | SYR4 |
| Lithium | 11.3 µg/L No EPA limit set Main supplier: CITY OF SAN MARCOS · 72,970 people · 2024 | 3/4 | UCMR-5 |
| Cyanide | 10 µg/L 5% of the EPA limit 200 µg/L Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019 | 1/4 | SYR4 |
| Bromoform | 8.6 µg/L No EPA limit set Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019
Highest in the ZIP: 9.889999999999992 µg/L — CRYSTAL CLEAR SUD · 20,766 people · 2019 | 4/4 | SYR4 |
| Dibromoacetic Acid | 6.369999999999998 µg/L No EPA limit set Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019
Highest in the ZIP: 9.04 µg/L — MAXWELL SUD · 16,104 people · 2019 | 4/4 | SYR4 |
| Trichloroacetic Acid | 8.6 µg/L No EPA limit set Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019 | 3/4 | SYR4 |
| Lead | 4.2 µg/L 28% of the EPA limit 15 µg/L Main supplier: CITY OF SAN MARCOS · 72,970 people · 2018
Highest in the ZIP: 7.313000000000011 µg/L — CRYSTAL CLEAR SUD · 20,766 people · 2019 | 4/4 | SYR4 |
| Selenium | 4.1 µg/L 8.2% of the EPA limit 50 µg/L Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019 | 1/4 | SYR4 |
| Monobromoacetic Acid | 2.164999999999999 µg/L No EPA limit set Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019
Highest in the ZIP: 3.990000000000001 µg/L — CRYSTAL CLEAR SUD · 20,766 people · 2019 | 3/4 | SYR4 |
| Xylenes, Total | 3.2 µg/L 0% of the EPA limit 10000 µg/L Highest in the ZIP: CRYSTAL CLEAR SUD · 20,766 people · 2019 | 1/4 | SYR4 |
| Arsenic | 2.2 µg/L 22% of the EPA limit 10 µg/L Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019 | 1/4 | SYR4 |
| Chromium | 1.9595 µg/L 2% of the EPA limit 100 µg/L Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019 | 1/4 | SYR4 |
| Dalapon | 1.59 µg/L 0.8% of the EPA limit 200 µg/L Highest in the ZIP: CRYSTAL CLEAR SUD · 20,766 people · 2019 | 1/4 | SYR4 |
| Combined Radium (-226 And -228) | 1.5 pCi/L 30% of the EPA limit 5 pCi/L Main supplier: CITY OF SAN MARCOS · 72,970 people · 2017 | 2/4 | SYR4 |
| Ethylbenzene | 1.1 µg/L 0.2% of the EPA limit 700 µg/L Highest in the ZIP: CRYSTAL CLEAR SUD · 20,766 people · 2019 | 1/4 | SYR4 |
| Di(2-ethylhexyl) Phthalate | 0.8700 µg/L 14% of the EPA limit 6 µg/L Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019 | 2/4 | SYR4 |
| Antimony, Total | 0.2220 µg/L 3.7% of the EPA limit 6 µg/L Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019 | 1/4 | SYR4 |
| Atrazine | 0.1600 µg/L 5.3% of the EPA limit 3 µg/L Main supplier: CITY OF SAN MARCOS · 72,970 people · 2019 | 1/4 | SYR4 |
| Pfba | 0.0114 µg/L No EPA limit set Main supplier: CITY OF SAN MARCOS · 72,970 people · 2024 | 2/4 | UCMR-5 |
| Pfpea | 0.0042 µg/L No EPA limit set Main supplier: CITY OF SAN MARCOS · 72,970 people · 2024 | 3/4 | UCMR-5 |
| Pfhxa | 0.0037 µg/L No EPA limit set Highest in the ZIP: MAXWELL SUD · 16,104 people · 2025 | 1/4 | UCMR-5 |
| PFHXS | 0.0034 µg/L No EPA limit set Main supplier: CITY OF SAN MARCOS · 72,970 people · 2024 | 1/4 | UCMR-5 |
| Lead | 0.0016 mg/L 11% of the EPA limit 0.0150 mg/L Main supplier: CITY OF SAN MARCOS · 72,970 people · 2024 | 4/4 | LCR |
Each bar shows the measured level as a share of the EPA limit: green is
well under, amber is close to it, red is over. For lead and copper the
limit applies to exactly the 90th-percentile figure shown, so red there
means a real exceedance. For everything else the limit applies to a
running annual average while the figure is the 95th percentile of the
system's samples — over 100% is worth reading, but is not by itself a
violation.
Formal violations are listed separately.
Water suppliers serving ZIP 78666
| Supplier | State | Population served |
|---|---|---|
| CITY OF SAN MARCOS | TX | 72,970 |
| TEXAS STATE UNIVERSITY - SAN MARCOS | TX | 43,552 |
| CRYSTAL CLEAR SUD | TX | 20,766 |
| MAXWELL SUD | TX | 16,104 |
Frequently asked questions about ZIP 78666 tap water
Is the tap water in ZIP 78666 safe to drink?
EPA testing detected 36 contaminants across the water suppliers serving ZIP 78666. A detection isn't the same as a violation — most levels are within federal limits. See each level and source above, and your utility's annual Consumer Confidence Report for the official status.
Which water suppliers serve ZIP 78666?
4 public water suppliers report EPA drinking-water monitoring for ZIP 78666. Each is listed above with its population served.
What contaminants are in ZIP 78666's water?
EPA monitoring detected Nitrate-Nitrite, Nitrate, Copper, Fluoride, Chlorite, and others across this ZIP's suppliers. The full list with levels and sources is above.