Well Water Notebook
Information only, not medical advice. We never say whether your water is safe to drink. Ask a state-certified lab or your local health department. Disclaimer

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Well water testing in Santa Clara County, California

In Santa Clara County, the local water district, Valley Water, issues well permits and offers free water testing for many domestic wells. Here's how to check if you qualify, what Valley Water says about nitrate, and where to find a lab or a licensed driller, with a source for every fact.

This page can't tell you whether your water is safe to drink. Only a test of your well can do that.

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How many people here use a private well

USGS estimates that about 45,000 people in Santa Clara County supplied their own household water in 2015, about 2% of the county's population.1

Free testing from Valley Water

Valley Water (the Santa Clara Valley Water District) offers to collect water samples from Santa Clara County homes served by domestic wells. Testing includes nitrate, bacteria, hardness, conductivity, fluoride, sulfate, chloride, bromide and orthophosphate.2

The State Water Board's directory also lists the Central Coast Drinking Water Well Testing Program for the southern portion of Santa Clara County: (844) 613-5152.3 If you rent out a home on a domestic well inside a program area, AB 2454 requires you to test through the program and share results with tenants within 10 days.4 See renting out a home on a well.

Nitrate in South County

Valley Water says nitrate is an ongoing groundwater protection challenge, particularly in South County, because of the valley's farming history and septic systems still in use. Shallow wells, wells near a source, wells in sandy soil and poorly built or maintained wells are more likely to be affected. California's limit is 45 mg/L as nitrate (10 mg/L as N); domestic wells aren't subject to drinking water standards, but Valley Water says those standards give context for your results. Boiling doesn't remove nitrate.5 See nitrate in well water.

Well permits

No one may drill, deepen, modify, repair or destroy a water well in Santa Clara County without first getting a permit from Valley Water. Valley Water says:6

For well treatment or septic system questions, Valley Water refers owners to the Santa Clara County Department of Environmental Health at (408) 918-3400.5

Buying a home with a well in Santa Clara County

We didn't find a statewide rule requiring a well test at sale; the Transfer Disclosure Statement asks whether the water supply is a well.7 Call Valley Water's hotline to see if the property qualifies for free testing, ask Valley Water about permits on file, and get a flow test. See buying a home with a well.

Get quotes from local well pros

Need a well drilled, a pump fixed, your water tested or treated, or a well inspected for a home sale in Santa Clara County, California? Tell us what you need. With your permission, we'll try to pass your request to up to 3 local licensed or certified providers. It's free. You can also look up licensed pros yourself in our directory.

Well Water Notebook is a free information site, not a contractor, and we can't guarantee anyone will contact you. We don't sell your details or add you to a mailing list. See our privacy policy.

Where to get tested and treatment options

Labs: see accredited labs in Santa Clara County, from the State Water Board's ELAP data. Confirm the lab is accredited for each test you need.8

Drillers: check a C-57 license with CSLB's Instant License Check.

Treatment: Valley Water points to the State Water Board's list of residential treatment systems certified to reduce nitrate, and recommends asking the vendor for assurance the system will work for your situation.5

  1. Dieter, C.A., and others, 2018, Estimated Use of Water in the United States County-Level Data for 2015 (ver. 2.0), U.S. Geological Survey data release. https://doi.org/10.5066/F7TB15V5 ↩

  2. Valley Water, "Free testing for domestic well owners." https://www.valleywater.org/your-water/groundwater/free-testing-domestic-well-owners ↩

  3. California State Water Resources Control Board, Well Testing Program Directory (spreadsheet, last updated June 2026). https://www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/docs/well-testing-program-directory.xlsx ↩

  4. California State Water Resources Control Board, "Rental Property Domestic Well Testing Requirements (AB 2454)." https://www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/private-domestic-well-testing.html ↩

  5. Valley Water, "Nitrate in groundwater." https://www.valleywater.org/accordion/nitrate-groundwater ↩↩↩

  6. Valley Water, "Well Permits and Inspections." https://www.valleywater.org/wells/well-permits-and-inspections ↩

  7. California Department of Real Estate, Disclosures in Real Property Transactions (RE 6). https://www.dre.ca.gov/files/pdf/re6.pdf ↩

  8. California State Water Resources Control Board, "Environmental Laboratory Accreditation Program (ELAP)." https://www.waterboards.ca.gov/drinking_water/certlic/labs/ ↩