Monterey County, California: drinking water report. Monterey County stretches from the Pacific coastline through Salinas, Carmel, Seaside, and inland…
Monterey County stretches from the Pacific coastline through Salinas, Carmel, Seaside, and inland agricultural communities to the eastern hills. Water comes from multiple sources including the Salinas River, Nacimiento Reservoir, local groundwater basins, and the Carmel River, with several dozen small water systems serving different parts of this geographically diverse county. The region's intensive agriculture and history of military operations have created distinct water quality challenges across urban and rural areas.
Monterey County faces documented contamination from multiple sources. The Salinas Valley aquifer system, which supplies much of the county's agricultural heartland and communities like Gonzales, Soledad, and King City, shows elevated nitrate levels from decades of fertilizer use. Some wells exceed the federal standard of 10 mg/L, particularly in rural areas with domestic wells outside municipal systems. The coastal strip faces different issues, with communities like Marina and Seaside dealing with legacy contamination from Fort Ord, where military operations left behind volatile organic compounds in groundwater.
PFAS testing under EPA's UCMR5 program revealed the chemicals in several California water systems, and Monterey County utilities likely detected these compounds given the state's widespread exposure patterns. The region's airports, former military sites, and industrial facilities all represent potential PFAS sources. California now regulates PFAS more strictly than federal standards, setting notification levels at 5-6 ppt for certain compounds and requiring public notification when these thresholds are exceeded.
Lead concerns exist primarily in older coastal communities where housing stock predates 1986 plumbing code changes. While the county's water itself typically shows low lead levels at treatment plants, the acidic nature of Carmel River water creates corrosion potential in distribution systems. Many smaller water districts lack comprehensive lead testing data from customer taps. Perchlorate, linked to rocket fuel and fireworks manufacturing, appears periodically in wells throughout the Salinas Valley.
Residents should request water quality reports from their specific provider, as conditions vary dramatically between the Salinas Valley, coastal communities, and southern county areas. Those on private wells face particular risks from nitrate contamination and should test annually. Check your water to see current contaminant data for your location, review our water filter guide for treatment options suited to your specific concerns, or access a detailed report with full testing data. For broader context on California's water quality regulations and statewide contamination patterns, visit our state page.
Drinking water is one exposure route. These federal datasets also cover Monterey County, CA.
The EPA places Monterey 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.
60% of homes in Monterey County, CA were built before 1980, and 14% 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 Monterey County, CA averages 5.2 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 133 public water systems serving Monterey County, CA with EPA lead testing on record, 9 (6.8%) reported a 90th-percentile lead result above the EPA's 15 ppb action level, and the median is 2.8 ppb. 53 water systems serving Monterey County, CA carry a health-based EPA Safe Drinking Water Act violation.
| Most-cited violation type | Systems affected |
|---|---|
| Lead and Copper Rule Revisions | 28 |
| Nitrate | 14 |
| Surface Water Treatment Rule | 7 |
| Arsenic | 5 |
| Total Coliform Rule | 4 |
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.