Last checked: October 22, 2026

Private well testing in California

Everything on this site for California private well owners, buyers, landlords and the pros who work with them: who permits wells, what the State Water Board says to test, free testing programs, certified labs, licensed drillers, well records, dry wells and groundwater rules. Every fact links to an official source.

California at a glance

• Who's on a well: USGS estimates about 1,436,000 Californians supplied their own household water in 2015, about 4% of the state's population. The counties with the most were Fresno (about 102,000), Contra Costa (about 89,000), Sonoma (about 77,000), San Joaquin (about 76,000) and Tulare (about 65,000).¹ The State Water Board says about 95% of Californians get their drinking water from a public or municipal source.²
• Water quality isn't regulated. The State Water Board says the State of California doesn't regulate the water quality in private domestic wells, and that the owner is responsible for maintaining the well and is encouraged to test it. Counties or local agencies may have their own requirements.²
• Wells are permitted locally. County environmental health agencies typically issue well construction, abandonment and destruction permits.² DWR's Bulletin 74 sets minimum statewide well standards, and local agencies (counties, cities and some water districts) enforce standards that are equal or stricter.³
• Small systems are different. Systems serving fewer than 15 connections ("state small water systems") may be regulated at the county level and required to sample their wells.²

What to test and how often

The State Water Board's guide for domestic well owners recommends, at a minimum, testing total coliform bacteria, nitrate and electrical conductivity (EC) every year, plus a mineral panel (including arsenic, iron, manganese, lead and others) every 5 to 10 years or when EC, taste, color, odor or nearby land use changes. It says basic analysis can range from $100 to $400.²

California's drinking water limits (MCLs) apply to public water systems, not private wells, but the State Water Board recommends comparing your results with them.² Some that matter for California wells:⁴

Where problems show up in public wells. The State Water Board's GAMA fact sheets, based on 2007–2017 data from public supply wells, list Los Angeles, Tulare and Kern as the counties with the most public wells over the nitrate MCL, and Kern, Fresno and Los Angeles as the counties with the most 1,2,3-TCP detections above the MCL. Data from private domestic wells isn't available in those summaries.⁸⁹

The GAMA program's online tools map groundwater quality data across the state.¹⁰

Free well testing programs

The State Water Board lists the domestic well testing and replacement drinking water programs it funds or regulates in a Well Testing Program Directory (spreadsheet, by county) and map. It says there are currently 11 such programs, run by nonprofits, regional groups or government agencies, and that services and eligibility vary; some offer bottled or hauled water or filters if a test finds a problem.¹¹ As of the June 2026 directory, programs cover parts or all of Fresno, Kern, Kings, Madera, Mariposa, Merced, Monterey, Riverside (eastern Coachella Valley), San Benito, San Joaquin, San Luis Obispo, San Mateo, Santa Barbara, Santa Clara, Santa Cruz, Stanislaus, Tulare, Ventura and Yolo counties.¹²

Open the Well Testing Program Directory and check that your address is inside the program's service area before you apply.

Renting out a home on a well (AB 2454)

Under AB 2454 (Lee, 2024), if a domestic well serves a rental property and the well is inside the boundaries of a free testing program funded or regulated by the State or a Regional Water Board, the owner must:¹¹

• test the well using the free testing program,
• share the results with tenants within 10 days of receiving them, with guidance on how to read them, and
• provide safe drinking water if results exceed drinking water standards and the program offers free replacement water.

Owners can't charge tenants or raise rent or fees for the testing or the replacement water. If the program doesn't offer free replacement water, the owner isn't required to pay for it out of pocket.¹¹ Sonoma County Environmental Health also notes that landlords are required to provide potable water to their tenants.¹³

Buying or selling a home with a well

California's Real Estate Transfer Disclosure Statement (Civil Code § 1102.6) has the seller check the property's water supply (city, well, private utility or other) and say whether any listed item isn't in operating condition.¹⁴ We didn't find a statewide rule that requires a well water test when a home is sold. Some counties have their own well rules, so ask the county environmental health department, and write a water test and well flow test into your offer. See buying a home with a well for what to order.

Certified labs

The State Water Board's Environmental Laboratory Accreditation Program (ELAP) accredits drinking water labs and maps them.¹⁵ Our California directory lists the commercial labs on ELAP's drinking water lab data, by county. The State Water Board's guide says it isn't always required to use a certified lab for a private well, and recommends getting quotes first.²

Licensed well drillers

Domestic wells must be drilled by a contractor with a C-57 Well Drilling license, and the driller needs a permit from the local permitting agency before construction, modification or destruction.² Check a license with CSLB's Instant License Check; CSLB's Public Data Portal offers a free list of licensees by classification and county.¹⁶

Well records (well completion reports)

Drillers record a well completion report (driller's log) that goes to the local permitting agency, DWR and the well owner.² DWR says drillers must submit well completion reports to DWR within 60 days.³ Look up a well with DWR's Well Completion Report Map Application, which also explains how to request a report you can't find.¹⁰

Dry wells and drought

If your private well goes dry or has problems, report it on DWR's Dry Well Reporting System, which is for Californians with private, self-managed wells. DWR says the reports inform state and local agencies about drought impacts and aren't an application for assistance; everything except the owner's name, contact information and address is visible to the public. As of October 22, 2026 the system showed 6,211 dry wells reported in total.¹⁷

Groundwater rules (SGMA)

Under the Sustainable Groundwater Management Act, a "de minimis extractor" is someone who pumps two acre-feet or less a year for domestic purposes.¹⁸ The State Water Board says most households use about a third of an acre-foot a year or less, that de minimis users are always exempt from extraction reporting in unmanaged areas, and that in a probationary basin they're generally exempt from reporting and fees unless the Board requires them to report because together they significantly affect the basin.¹⁹²⁰ Local Groundwater Sustainability Agencies (GSAs) may have their own requirements for new wells; Fresno County, for example, tells owners in critically overdrafted subbasins to check with their GSA before drilling.²¹

County pages

• Well water testing in Fresno County, CAFresno County private wells: who issues well permits, free well testing programs, what the State Water Board says to test, 1,2,3-TCP and nitrate data, labs and C-57 drillers, with sources.Last checked 2026-10-22
• Well water testing in Santa Clara County, CASanta Clara County private wells: Valley Water's free domestic well testing and well permits, nitrate in South County, the Central Coast testing program, labs and C-57 drillers, with sources.Last checked 2026-10-22
• Well water testing in Sonoma County, CASonoma County private wells: Permit Sonoma's well permits and 2023 well ordinance, dry weather well testing, metering rules, the county's testing schedule, PFAS sampling advice, labs and C-57 drillers, with sources.Last checked 2026-10-22
• Well water testing in Tulare County, CATulare County private wells: well permits, the county's voluntary water testing program, free testing and replacement water programs, nitrate, DBCP and radiological tests, labs and drillers, with sources.Last checked 2026-10-22

Guides for California well owners

• Buying a home with a well
• Nitrate in well water
• Arsenic in well water
• Uranium and radon in well water
• Getting a new well drilled
• How to read your well water test results
• For professionals: selling a home with a well (realtors) and homes with a well (home inspectors)