Private well guide

Well Water in California: Testing, Rules, Labs and Licensed Contractors

574,203 households in California get their water from a private well. Here is what the state requires, where to get it tested, and who is licensed to work on it.

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708Licensed contractorschecked against state records
101Certified labsfrom the state certified list
58Counties covered
574,203Households on wells4% of households (est.)

Only about 4% of California households are on a private well, but in a state of 39 million people that is still more than half a million homes, most of them in the foothills, the Central Valley and the far north. California leaves the well itself to the county and the water to you, and it keeps the best public record of any state: a completion report for more than a million wells that anyone can read.

Who is in charge of a California well

The state sets the standard and the county enforces it. Under the Water Code every county (and a few cities and water districts) is the permitting agency for wells, working from the California Well Standards in DWR Bulletin 74. Your county environmental health department issues the permit, inspects the seal and, in most counties, asks for a bacteriological sample before it closes the file. The driller must hold a C-57 Well Drilling license from the Contractors State License Board, which also covers pump work, and must send a Well Completion Report to the Department of Water Resources within 60 days. Those reports are public: the depth, casing, seal, yield and geology of your well are probably online already. The State Water Resources Control Board sits above all of it, accrediting the labs through ELAP and running the nitrate and safe-water programs in the valleys.

What is required, and what is left to you

A county permit, a licensed driller, construction to Bulletin 74 and the completion report. After that, nothing: California does not require a test of private well water when the well is new, when the house is sold or at any time in between, apart from the bacteriological sample most counties want at completion. The State Water Board’s advice is a test every year. Bacteria and nitrate are the minimum; in the valleys and foothills a first test should add arsenic, uranium, chromium and 1,2,3-TCP, because those are the contaminants that have forced whole towns onto bottled water.

At a glance

Water test for a new wellNot required statewide

No statewide water test. State law (Water Code 13801) makes the county the permitting agency: you need a well permit from the county environmental health department before drilling, the well must be built to the California Well Standards in DWR Bulletin 74 (annular seal, setbacks from septic systems and property lines, disinfection) by a C-57 licensed contractor, and the driller files a Well Completion Report with the Department of Water Resources within 60 days. Most counties require a bacteriological sample, and some add nitrate, before they sign off the permit, so check your county's well ordinance.

Water test when a home is soldNot required statewide

No statewide requirement. The Transfer Disclosure Statement only says whether the property is on a well. FHA, VA and USDA loans normally require a bacteria, nitrate and lead sample from an accredited lab before closing, and a handful of counties and cities (Santa Cruz County among them) require a well inspection or test at transfer.

What the state recommends

The State Water Board recommends testing a domestic well every year. Bacteria and nitrate are the yearly minimum; a first test should add arsenic, uranium, hexavalent and total chromium, 1,2,3-TCP, fluoride, hardness, iron, manganese, sodium, boron and total dissolved solids, with perchlorate and PFAS where the county or a nearby public system has found them. Test again after a flood, a wildfire, well work or a change in taste, color or smell, and check the level in dry years.

Free or low-cost testingAvailable

In the San Joaquin and Sacramento valleys the nitrate management zones set up under the Central Valley Water Board's Nitrate Control Program test private wells for free and supply bottled water where nitrate is over the limit: the Valley Water Collaborative covers the Modesto, Turlock, Eastern San Joaquin, Delta-Mendota, Merced, Madera and Yolo basins ((209) 750-3867), and the Kings, Kaweah, Tule and Chowchilla zones run similar programs through Self-Help Enterprises. Several counties (Santa Clara Valley Water and Sonoma County among them) run free or reduced-cost domestic well testing days. Elsewhere, county public health labs run a bacteria test for roughly $30 to $60.

What the water is like

California’s groundwater is as varied as its geology. The San Joaquin Valley is the hardest place in the country to own a well: nitrate from a century of farming, arsenic in the Tulare Lake basin and along the west side, uranium in the sediments washed out of the Sierra, and 1,2,3-TCP and DBCP left over from soil fumigants. The Sierra foothills give clean, often soft water from fractured granite, but uranium and radon come with the granite and yields drop in dry years. The Sacramento Valley and the North Coast are gentler, with shallow wells and iron and manganese as the usual complaints. The Coast Ranges run hard and salty, the deserts add fluoride, boron and arsenic, and the Inland Empire has perchlorate and hexavalent chromium plumes. Every one of these shows up in a first-time broad test, which is why the state pushes for one.

ELAP-accredited labs and county public health labs

California accredits environmental labs through the Environmental Laboratory Accreditation Program, and each lab’s certificate lists exactly which drinking water tests it may run. The labs below hold current accreditation for at least the tests a well owner needs. County public health laboratories run the bacteria test cheaply and often nitrate too; the commercial labs handle the arsenic, uranium, chromium and TCP panel, and most will mail bottles anywhere in the state.

101 certified labs

See all 101 certified labs in California

C-57 licensed well drillers

Every contractor below holds an active C-57 Well Drilling license, checked against the Contractors State License Board list. Because DWR publishes every well completion report with the driller’s license number, each profile also shows how many wells the company has reported since 2016, how many were domestic supply, and which counties it works in, which is the most reliable guide to who is actually drilling near you. The license covers pump installation and repair as well as drilling and well destruction.

708 licensed contractors

See all 708 licensed contractors in California

By county

Well use runs from almost nobody in Los Angeles, Orange and the Bay Area counties to a third or more of all homes in Siskiyou, Lassen, Lake and Trinity counties, half in Tehama and Modoc, and about seven in ten in Mariposa. Each county page carries its well population, the typical depth of domestic wells drilled there since 2000, the nearest accredited labs and the licensed drillers based there.

California well water questions

Do I need a permit to drill a well in California?

Yes, from your county environmental health department (or the city or water district that holds the well ordinance where you live). The permit sets the construction standard, the setbacks and any water test the county wants before it signs off. Your C-57 contractor normally pulls it.

Is a water test required when I sell my house?

No statewide. Lenders on government-backed loans require a bacteria, nitrate and lead test before closing, and a few counties and cities require a well inspection at transfer, so ask your county.

How do I find the record for my well?

Search the DWR Well Completion Report dataset on the state open data portal by county, city or address, or use the Online System for Well Completion Reports map. Wells drilled since the late 1980s are almost always there; older ones often are.

Can I get my well tested for free?

In the Central Valley nitrate management zones, yes: the Valley Water Collaborative and the Kings, Kaweah, Tule and Chowchilla programs test domestic wells at no charge and provide bottled water where nitrate is over the limit. Some counties and water districts run free testing days. Everywhere else, a county public health lab bacteria test is the cheapest option.

Which lab should I use?

Any lab on the ELAP list whose accreditation covers the test you need. Use a county public health lab for the yearly bacteria check and a commercial lab for the metals, uranium, chromium and TCP panel.