Santa Clara County, California: drinking water report. Santa Clara County – Silicon Valley – is home to about 1.9 million residents served by multiple
Santa Clara County – Silicon Valley – is home to about 1.9 million residents served by multiple water agencies including the Santa Clara Valley Water District, San Jose Water Company, and several smaller utilities. The water supply is a blend of imported water from the State Water Project and Central Valley Project, local reservoir storage, recycled water, and groundwater from the Santa Clara Valley subbasin.
Silicon Valley's decades of semiconductor and electronics manufacturing left a legacy of groundwater contamination that the county is still managing. The EPA lists 23 Superfund sites in Santa Clara County – one of the highest concentrations in any US county – many related to solvent and chemical spills from tech manufacturing. While most of these sites are in active remediation, some contaminants persist in the groundwater.
PFAS compounds have been detected in UCMR5 sampling across multiple county water systems. Moffett Federal Airfield, managed by NASA Ames Research Center, is a documented PFAS source. According to the California State Water Resources Control Board, 16 public water systems in Santa Clara County reported PFAS detections during the most recent monitoring period.
Silicon Valley's contamination legacy is primarily a groundwater issue. If your water provider draws from local wells near Superfund sites or Moffett Field, your risk profile differs from homes served primarily by imported surface water.
Check your water to see monitoring data for your specific provider and area. Reverse osmosis filters handle the broadest range of contaminants found in this county. Our water filter guide details which systems are certified for PFAS and volatile organic compounds. Pull your detailed report for trend data, and see our California page for statewide context.
Drinking water is one exposure route. These federal datasets also cover Santa Clara County, CA.
The EPA places Santa Clara County, CA in Zone 2 - a moderate-risk category, with a predicted average indoor radon level between 2 and 4 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.
61% of homes in Santa Clara County, CA were built before 1980, and 8% 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 Santa Clara County, CA averages 7.9 µg/m³, within 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 95 public water systems serving Santa Clara County, CA with EPA lead testing on record, 6 (6.3%) reported a 90th-percentile lead result above the EPA's 15 ppb action level, and the median is 2.5 ppb. 30 water systems serving Santa Clara County, CA carry a health-based EPA Safe Drinking Water Act violation.
| Most-cited violation type | Systems affected |
|---|---|
| Total Coliform Rule | 10 |
| Surface Water Treatment Rule | 7 |
| Nitrate | 4 |
| Haloacetic Acids (HAA5) | 3 |
| Revised 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.