Arsenic and manganese are worth checking in Nevada County wells.
2 worth checking, 5 rare out of 7 health checks.
From 58 wells tested in Nevada County since 2007; 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 2 people 48,312 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 Nevada County compares with California and the counties around it.
Each result puts Nevada County next to the 4 counties that border it, on the chart's 0 to 50% scale.
These 2 are worth checking in Nevada County.
Arsenic3 of 58 wells over
Too few tested to show: Sierra.
Manganese3 of 58 wells over
Too few tested to show: Sierra.
These 5 are rare in Nevada County.
Nitrate0 of 58 wells over
Too few tested to show: Sierra.
Uranium0 of 58 wells over
Too few tested to show: Sierra.
Radon in water0 of 14 wells over
Too few tested to show: Sierra, Yuba.
Fluoride0 of 58 wells over
Too few tested to show: Sierra.
Lead0 of 37 wells over
Too few tested to show: Sierra, Yuba.
Coliform bacteria turned up in 7 of 40 tested Nevada County wells, so test for it every year.
Coliform bacteria7 of 40 wells had it
Too few tested to show: Sierra.
E. coli3 of 40 wells had it
Too few tested to show: Sierra.
E. coli means human or animal waste is getting in, so if a test of your Nevada County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 6 of 58 tested wells, and it isn't a health risk.
Iron stains6 of 58 wells had it
Too few tested to show: Sierra.
Nevada County has 58 tested wells, and the busiest decade for testing was the 2010s.
Only 11 of the 58 wells have a test from 2020 or later, so a fresh test of your own well tells you more than any of these.
Most Nevada 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 4 things to check in Nevada County.
- Bacteria
- Nitrate
- Arsenic
- Manganese
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 220 feet.
That comes from 21,399 household wells in California's drilling records. Most wells of every kind here are 130 to 360 feet deep. Wells as deep as Nevada 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 33 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 Nevada County.
Nevada 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 6 town water systems in Nevada 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 4.6 ng/L of PFOA. Only 10 wells in Nevada 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 Nevada County
Is well water in Nevada County safe to drink?
3 of 58 wells tested in Nevada County had arsenic over the limit, about 1 in 19. Across California it's about 1 in 7. That's a smaller share than in 33 of the 46 other California counties with 10 or more tested wells. So test your own well for arsenic before you count on it.
Can I get my well tested for free in Nevada 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, arsenic and manganese, the tests that matter most in Nevada County.
How deep are wells in Nevada County?
Half the household wells here are shallower than 220 feet. Typical household wells here go deeper than in 33 of the 56 other California counties with enough drilling records.
How does Nevada County compare with the counties around it?
For arsenic, the share of tested wells over the limit: 1 of the 3 neighboring counties with data had a higher share than Nevada County, at 5%. Washoe, NV had the most, at 35%. Groundwater doesn't stop at county lines, so Washoe, NV's 35% is worth knowing about if you live near it.
How often should I test my well in Nevada County?
In Nevada County, 7 of 40 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 Nevada County numbers come from
- People on wells: 48,312 in Nevada County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 567 well water samples from 58 wells in the Water Quality Portal, run by the USGS and EPA, 2007 to 2022.
- Well depths: 21,399 California drilling records for Nevada County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 4 counties that share a border with Nevada County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 6 town water systems in Nevada County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Nevada County is zone 2 on the EPA Map of Radon Zones.
- State programs and links: State Water Resources Control Board, checked November 1, 2026.