Is San Marcos, CA tap water safe?
Data: U.S. EPA · How we read the data · How we check it
Summary
No federal limits exceeded in EPA data for Vista Irrigation District.
2 public water systems serve parts of San Marcos. The largest, Vista Irrigation District, serves 134,501 people. Your water bill names your system.
Largest system
Vista Irrigation District
134,501 people · Surface water · EPA ID CA3710027
Buys treated water from City of Oceanside, Vallecitos Water District, San Diego County Water Authority, City of Escondido.
| PFAS | Highest average | Limit |
|---|---|---|
| PFOA Not detected | – | 4 ppt |
| PFOS Not detected | – | 4 ppt |
| PFHxS Not detected | – | 10 ppt |
| PFNA Not detected | – | 10 ppt |
| HFPO-DA (GenX) Not detected | – | 10 ppt |
ppt = parts per trillion. "Highest average" is the highest average at any of the system's entry points, the way EPA compares results with the limits.
Lead: 0 ppb at the 90th percentile (Dec 2024, and 9 in 10 homes sampled were at or below it) Below action level
Health-based violations since 2016: 0
Across California, 129 of 691 water systems EPA tested had PFAS above a 2024 federal limit, and 26 systems were above the lead action level in results from the last five years. California results.
San Marcos homes and lead pipes
Lead service lines and lead solder were allowed until 1986, so homes from before then are the ones to check. Renting? Ask your landlord what the service line is made of, because it's their pipe to replace. How to check your own line.
Housing: Census American Community Survey 2020–2024 5-year estimates for San Marcos city (tables B25034, B25003). Estimates for small places have a margin of error.
Other water systems serving San Marcos
How nearby cities compare
| City | PFAS | Lead (90th pct.) |
|---|---|---|
| Escondido 6 mi City of Escondido | None above limits | 1.1 ppb |
| Vista 6 mi Vista Irrigation District | None above limits | 0 ppb |
| Carlsbad 7 mi Carlsbad Municipal Water District | None above limits | 0 ppb |
| Encinitas 8 mi Olivenhain Municipal Water District | None above limits | 0 ppb |
| Oceanside 10 mi City of Oceanside | None above limits | 0 ppb |
| Poway 13 mi City of Poway | None above limits | 0 ppb |
San Marcos ZIP codes (2)
- 92069
- 92078
Questions
Is San Marcos tap water safe to drink?
Vista Irrigation District has had no health-based violations since 2016. Utility data can't show lead from your own pipes: if your home was built before 1986, test your tap. Your utility's annual Consumer Confidence Report is the official summary.
Who supplies water in San Marcos, CA?
2 public water systems serve parts of San Marcos. The largest is Vista Irrigation District (134,501 people). Your water bill names your system. The EPA ID is also on your utility's Consumer Confidence Report.
Does San Marcos tap water have PFAS?
None detected above EPA's reporting limits. Vista Irrigation District had no PFAS detected in EPA's 2023–2025 testing. "Not detected" means below the reporting limit (about 2 to 20 ppt), not proven zero.
Do San Marcos homes have lead pipes?
Census estimates put 27% of San Marcos homes as built before 1980 (California: 56%). Lead service lines and lead solder were allowed until 1986, so older homes are more likely to have them. Vista Irrigation District's service line inventory says what your line is made of. The only way to know for your home is to check the line where it enters the house and test your tap.
Source: U.S. EPA drinking water records and PFAS testing (UCMR 5). How we read the data.