California county well guide

Well Water in Contra Costa County, CA: Testing, Contractors and Rules

About 35,549 households in Contra Costa County, 8% of the county, rely on a private well. Nobody tests that water unless the owner does.

Labs within 40 milesLicensed contractors
8%of households on a private well
Share on wells, county vs state
Contra Costa County8%
California average4%
47licensed contractors serve the county
15 mito the nearest certified lab, Alameda County Public Health Laboratory
Nostatewide test required when a home is sold

About 35,549 homes in Contra Costa County are on a private well. That is 8% of households, enough that every township has well owners and few of them have had the water tested recently.

Local rules for wells in Contra Costa County

The rules that apply in Contra Costa County are set at the state level in California. The state does not require a test on a new well, and nothing is required at sale. Some counties and townships add permits or setbacks of their own, so check locally before drilling. The state's own recommendations are below.

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.

Getting your water tested near Contra Costa County

The nearest certified lab is Alameda County Public Health Laboratory in Oakland, about 15 miles from the county center, and it accepts samples from homeowners. There are 10 more within 40 miles, listed below with what each tests for.

11 certified labs within 40 miles

Licensed well contractors serving Contra Costa County

Licensed help in Contra Costa County includes Altamont Water Well and Pump and American Construction and Supply Inc and 45 others. Every listing was matched to the California license list; the "verify" link on each profile opens the state lookup.

Well depth and water chemistry

Well depth and water chemistry in Contra Costa County follow the rock underneath it. Typical wells here run 160 to 300 feet; the median of 876 domestic wells reported to DWR since 2000 is 230 feet feet. Contaminants worth testing for in this part of California include nitrate (san joaquin valley, salinas valley, dairy and orchard country), arsenic (tulare lake basin.

Typical well depth

160 to 300 feet; the median of 876 domestic wells reported to DWR since 2000 is 230 feet feet

Contaminants to test for
  • Nitrate (San Joaquin Valley
  • Salinas Valley
  • Dairy and orchard country)
  • Arsenic (Tulare Lake basin
  • Western San Joaquin Valley
  • The deserts)
  • Uranium (eastern San Joaquin Valley
  • Sierra foothill granite)
  • Hexavalent chromium (Coachella Valley
  • Parts of the Central Valley)
  • 1
  • 2
  • 3-TCP and DBCP (former fumigated farmland in the Central Valley)
  • Coliform bacteria (shallow foothill and coastal wells near septic systems)
  • Hardness and total dissolved solids (Coast Ranges
  • Desert basins)
  • Iron and manganese (Delta
  • Coastal alluvium)
  • Fluoride and boron (Kern
  • Imperial
  • Desert basins)
  • Perchlorate (Inland Empire)
  • PFAS near airfields and industrial areas

Neighboring counties: Alameda County, Solano County, San Francisco County, Marin County.

What well work costs in Contra Costa County

Basic bacteria and nitrate test$25 to $75lab fee, homeowner sample
Full panel lab test$150 to $400metals, VOCs, radiologicals
Well inspection$250 to $550flow, pressure, visual, water test
Submersible pump replacement$1,200 to $4,500parts and labor
Pressure tank replacement$400 to $1,200installed
Whole-house treatment system$800 to $6,000softener, iron filter, UV, RO
New well drilled$5,500 to $25,000about $25 to $65 per foot
Shock chlorination$80 to $300or about $20 as a DIY job

National ranges from published 2025 to 2026 contractor pricing. Local quotes vary with depth, access and materials.

Questions Contra Costa County well owners ask

How many homes in Contra Costa County are on a well?

About 35,549, or 8% of households, based on Census housing data and state well surveys. The share is highest outside the towns with public water.

Where is the closest certified lab to Contra Costa County?

Alameda County Public Health Laboratory in Oakland, about 15 miles away. It accepts homeowner samples.

Do I need a permit to drill a well in Contra Costa County?

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.

What does a well test cost near Contra Costa County?

A bacteria and nitrate test runs $25 to $75 at most certified labs; a full panel with metals is $150 to $400. Mail-in kits cost about the same as walking in.