Arsenic in California well water

In California, 15% of 18,251 tested private well samples exceeded the EPA limit for arsenic (10 ug/L).

Arsenic occurs naturally in New England bedrock and dissolves into well water. Long-term exposure raises the risk of bladder, lung and skin cancers, and is linked to heart disease and lower IQ in children. It has no taste or smell, so testing is the only way to know.

Check your arsenic number

Type the value from your lab report. It is compared to the EPA limit, the same way the full interpretation does it.

Test your California well for arsenic

Certified lab analysis of your own tap water, bottles and prepaid return shipping included. The Essential well panel covers arsenic, uranium, nitrate, lead, copper, manganese, iron, sodium and bacteria; radon and PFAS are add-ons.

Order the Tap Score well water test kit, from $209 Already tested? Upload the report

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Systems that remove arsenic

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For arsenic

Under-sink reverse osmosis system

under-sink or countertop, about $300

Look for NSF/ANSI 58 certification listing the contaminant you need removed.

For arsenic

Whole-house arsenic and uranium filter

whole-house, at the point of entry, about $2,500

Adsorptive iron-based media; sized to your well yield.

For arsenic

Aquasana SmartFlow reverse osmosis

under-sink or countertop, about $225

Certified to NSF/ANSI 58 and 53 to reduce arsenic (96%, pentavalent), fluoride (90%), lead (99%), nitrate, nitrite and PFOA/PFOS at the kitchen tap, with a remineralizer.

Rather have it installed and sized for your well? Book a free in-home water test with a licensed local company.

Where to get a well tested for arsenic in California: certified labs, state programs and prices.

By county, from individual samples

Public monitoring samples against the EPA limit (10 ug/L); counties with at least 30 samples.

County	Above EPA limit	Samples	Detected	Median	Highest
Mono	69%	458	97%	59.8	2,200 ug/L
Kings	35%	185	93%	6	2,600 ug/L
Kern	32%	1,112	93%	5	4,000 ug/L
Sutter	28%	137	97%	8	100 ug/L
San Joaquin	23%	461	98%	4	66.8 ug/L
Napa	23%	83	94%	4.5	128 ug/L
San Bernardino	23%	4,608	90%	2.5	970 ug/L
Imperial	22%	106	97%	3.05	160 ug/L
Sacramento	18%	370	99%	3.7	120 ug/L
Los Angeles	17%	1,129	87%	1.6	353 ug/L
Inyo	15%	117	92%	1.9	7,500 ug/L
Mendocino	14%	133	67%	0.17	85.2 ug/L
Madera	13%	216	99%	2	89.8 ug/L
Tulare	10%	463	85%	1.2	230 ug/L
Lassen	9%	53	98%	2.7	240 ug/L

Mammoth Lakes CCD, Mono County70% of 448
Earlimart CCD, Tulare County60% of 45
Newberry Springs-Baker CCD, San Bernardino County54% of 758
Searles Valley CCD, San Bernardino County52% of 42
Thornton CCD, San Joaquin County50% of 32
Hanford CCD, Kings County46% of 46
Buttonwillow CCD, Kern County45% of 47
Arvin-Lamont CCD, Kern County43% of 63
North Antelope Valley CCD, Los Angeles County43% of 340
Manteca CCD, San Joaquin County43% of 47
Coachella Valley CCD, Riverside County41% of 76
East Kern CCD, Kern County41% of 474
West Kern CCD, Kern County40% of 95
Meridian-Robbins CCD, Sutter County38% of 37
Stratford CCD, Kings County37% of 78
Oakhurst-North Fork CCD, Madera County37% of 60
Hopland CCD, Mendocino County36% of 33
Stockton CCD, San Joaquin County35% of 167
Barstow CCD, San Bernardino County29% of 963
Wasco CCD, Kern County28% of 124

Sources

Individual samples from the USGS Water Quality Portal and state monitoring, summarized per geography. arsenic counts and shares are listed on each county and town page with their sources.

Analysis: Arsenic in private wells, state by state, from the same public records.