Nitrate is widespread in Monterey County wells.
1 widespread, 2 worth checking, 4 rare out of 7 health checks.
From 80 wells tested in Monterey County since 2000; your own well needs its own test. How to read this
Rare: under 5%Worth checking: 5 to 15%Widespread: 15%+
Lab results: Water Quality Portal (USGS and EPA)
Who drinks from a well here
1 in 10 people 43,611 people
Nobody else tests these wells. Only you do.
People on wells: EPA researchers' 2020 estimate
How deep wells go here
Deep wells: fewer surface germs, more minerals from the rock.
Well depths: US Groundwater Well Database
Radon risk (a gas from rock)
Possible here. A home air test is inexpensive.
Radon zones: EPA map
Here's how Monterey County compares with California and the counties around it.
Each result puts Monterey County next to the 5 counties that border it, on the chart's 0 to 50% scale.
This one is widespread in Monterey County wells.
Nitrate15 of 80 wells over
These 2 are worth checking in Monterey County.
Uranium5 of 76 wells over
Manganese4 of 80 wells over
These 4 are rare in Monterey County.
Arsenic1 of 80 wells over
Radon in water0 of 53 wells over
Too few tested to show: Kings, San Benito.
Fluoride0 of 80 wells over
Lead0 of 71 wells over
Coliform bacteria turned up in 3 of 23 tested Monterey County wells, so test for it every year.
Coliform bacteria3 of 23 wells had it
Too few tested to show: San Luis Obispo, Santa Cruz.
E. coli0 of 23 wells had it
Too few tested to show: San Luis Obispo, Santa Cruz.
E. coli means human or animal waste is getting in, so if a test of your Monterey County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 5 of 78 tested wells, and it isn't a health risk.
Iron stains5 of 78 wells had it
Monterey County has 80 tested wells, and the busiest decade for testing was the 2010s.
Only 17 of the 80 wells have a test from 2020 or later, so a fresh test of your own well tells you more than any of these.
Most Monterey County wells in these records were tested for research or because someone suspected a problem, which can push the shares above what a typical home well would show (how we read the numbers).
One mail-in lab test covers the 5 things to check in Monterey County.
- Bacteria
- Nitrate
- Uranium
- Manganese
- Arsenic
What California offers well owners
- Free testingThe State and Regional Water Boards fund or regulate 11 domestic well programs that offer free well testing in their service areas. See the program
- Certified labsCalifornia's list of certified labs
- Well recordsCalifornia's well record search
Half the household wells here are shallower than 300 feet.
That comes from 5,179 household wells in California's drilling records. Most wells of every kind here are 150 to 460 feet deep. Wells as deep as Monterey County's are usually better protected from fertilizer and bacteria at the surface, but they can pick up more of what's in the rock, like arsenic and uranium. Typical household wells here go deeper than in 47 of the 56 other California counties with enough drilling records.
Look up your own well's depth in California's well record search, or see how to find it.
Well depths: US Groundwater Well Database
Here's what we know about radon and PFAS in Monterey County.
Monterey County is in the EPA's middle radon zone. An indoor air test is cheap and tells you whether to look at your water. Radon guide
Between 2023 and 2025 the EPA had 16 town water systems in Monterey County test for PFAS. 1 of them had at least one test above 4 ng/L, the new EPA limit for PFOA and PFOS. The highest single result was 8.1 ng/L of PFOA. Only 17 wells in Monterey County have public PFAS results, so the town systems are the best clue to what's in the groundwater nearby. PFAS guide
Radon zones: EPA Map of Radon Zones. PFAS: EPA tests of town water systems, 2023 to 2025
Questions people ask about well water in Monterey County
Is well water in Monterey County safe to drink?
15 of 80 wells tested in Monterey County had nitrate over the limit, about 2 in 10. Across California it's about 1 in 10. That's a bigger share than in 41 of the 46 other California counties with 10 or more tested wells. So test your own well for nitrate before you count on it.
Can I get my well tested for free in Monterey County?
The State and Regional Water Boards fund or regulate 11 domestic well programs that offer free well testing in their service areas. If not, use a lab California has certified for drinking water. Ask for bacteria, nitrate, uranium, manganese and arsenic, the tests that matter most in Monterey County.
How deep are wells in Monterey County?
Half the household wells here are shallower than 300 feet. Typical household wells here go deeper than in 47 of the 56 other California counties with enough drilling records.
How does Monterey County compare with the counties around it?
For nitrate, the share of tested wells over the limit: 1 of the 5 neighboring counties with data had a higher share than Monterey County, at 19%. Fresno had the most, at 29%. Groundwater doesn't stop at county lines, so Fresno's 29% is worth knowing about if you live near it.
How often should I test my well in Monterey County?
In Monterey County, 3 of 23 tested wells had coliform bacteria, so the CDC's advice matters here: test for bacteria and nitrate every year, and right away after a flood, a repair, or any change in taste or smell.
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Where the Monterey County numbers come from
- People on wells: 43,611 in Monterey County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 862 well water samples from 80 wells in the Water Quality Portal, run by the USGS and EPA, 2000 to 2023.
- Well depths: 5,179 California drilling records for Monterey County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 5 counties that share a border with Monterey County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 16 town water systems in Monterey County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Monterey County is zone 2 on the EPA Map of Radon Zones.
- State programs and links: State Water Resources Control Board, checked November 1, 2026.