San Diego County, California: drinking water report. San Diego County imports roughly 85% of its drinking water from the Colorado River and Northern…
San Diego County imports roughly 85% of its drinking water from the Colorado River and Northern California, supplemented by the Carlsbad Desalination Plant and a growing recycled water program. The county's 3.3 million residents are served by over 20 water agencies, each with distinct source blends and treatment approaches. The Pure Water San Diego program aims to produce 83 million gallons per day of purified recycled water by 2035, but today most taps still deliver conventionally treated imported water.
San Diego County hosts multiple Navy and Marine Corps installations – Naval Base San Diego, MCAS Miramar, and NAS North Island among them – all of which have documented histories of AFFF firefighting foam use. The Department of the Navy has confirmed PFAS contamination at several of these sites. The EPA's UCMR5 data shows detections across county water systems, though systems receiving desalinated water from Carlsbad (which uses reverse osmosis) tend to test significantly cleaner for PFAS.
California's notification levels of 5.1 ppt for PFOA and 6.5 ppt for PFOS are among the strictest in the nation. According to the San Diego Regional Water Quality Control Board, 14 public water systems in the county reported PFAS detections above notification thresholds during 2024 monitoring.
Which water agency serves your home matters enormously. Coastal communities may receive more desalinated water in their blend, while inland areas rely more heavily on imported Colorado River water with conventional treatment.
Check your water to see data specific to your ZIP code and provider. If PFAS levels are elevated, a reverse osmosis system under the sink handles the broadest range of contaminants. Our water filter guide breaks down which certifications actually mean something versus marketing noise. For historical data and trends, pull your detailed report. See our California page for statewide context.
Drinking water is one exposure route. These federal datasets also cover San Diego County, CA.
The EPA places San Diego County, CA in Zone 3 - the EPA's lowest-risk category, with a predicted average indoor radon level below 2 pCi/L. Zone maps predict an area's radon potential from geology and existing indoor readings; they say nothing about a specific house. Testing is the only way to know your own level.
51% of homes in San Diego County, CA were built before 1980, and 7% before 1950. Residential lead paint was banned in 1978, so housing age is the strongest available proxy for lead-paint exposure. This describes the county's housing stock, not any one home.
Modelled annual fine-particle pollution (PM2.5) in San Diego County, CA averages 9.1 µg/m³, above the EPA's annual standard of 9 µg/m³. These are CDC modelled county estimates rather than readings from a specific monitor.
How radon zones work · Air quality by county · Lead exposure guide
Across 83 public water systems serving San Diego County, CA with EPA lead testing on record, 10 (12%) reported a 90th-percentile lead result above the EPA's 15 ppb action level, and the median is 2.8 ppb. 31 water systems serving San Diego County, CA carry a health-based EPA Safe Drinking Water Act violation.
| Most-cited violation type | Systems affected |
|---|---|
| Revised Total Coliform Rule | 9 |
| Nitrate | 7 |
| Combined Uranium | 5 |
| Lead and Copper Rule Revisions | 4 |
| Total Coliform Rule | 3 |
Source: EPA Lead and Copper Rule 90th-percentile tap sampling and EPA SDWIS Safe Drinking Water Act enforcement records, aggregated from the public water systems serving this county. Figures are counts of water systems, not a test of any individual home or tap.