California county well guide

Well Water in Mendocino County, CA: Testing, Contractors and Rules

About 9,991 households in Mendocino County, 29% of the county, rely on a private well. Nobody tests that water unless the owner does.

Labs within 40 milesLicensed contractors
29%of households on a private well
Share on wells, county vs state
Mendocino County29%
California average4%
24licensed contractors serve the county
14 mito the nearest certified lab, Alpha Analytical Laboratories, Inc. – Ukiah
Nostatewide test required when a home is sold

Mendocino County has an estimated 9,991 households on private wells, 29% of the county. If you are one of them, testing, treatment and repairs are yours to arrange.

Local rules for wells in Mendocino County

Private wells in Mendocino County follow California's statewide rules, administered by County environmental health departments issue well permits and enforce the state well standards. No water test is required by the state when a new well is completed. There is no statewide test requirement when a home is sold, though lenders often ask for one. The cards below show the details and the official sources.

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 Mendocino County

1 certified lab within 40 miles serves Mendocino County, starting with Alpha Analytical Laboratories, Inc. – Ukiah in Ukiah (about 14 miles from the county center). Each card below shows whether the lab takes homeowner samples and which tests it is certified for.

1 certified labs within 40 miles

Licensed well contractors serving Mendocino County

24 licensed contractors serve Mendocino County, including Clear Heart Drilling Inc and Confluence Environmental Inc. Each profile carries the state license number and the date we checked it, and the filters below sort them by drilling, pump work or treatment.

Well depth and water chemistry

Wells in Mendocino County typically reach 140 to 220 feet; the median of 3,496 domestic wells reported to DWR since 2000 is 180 feet. What comes up with the water depends on the aquifer, and across California the usual suspects are nitrate (san joaquin valley, salinas valley, dairy and orchard country), arsenic (tulare lake basin. A first full panel tells you which of them apply to your well.

Typical well depth

140 to 220 feet; the median of 3,496 domestic wells reported to DWR since 2000 is 180 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: Lake County, Glenn County, Sonoma County, Colusa County.

What well work costs in Mendocino 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 Mendocino County well owners ask

How many homes in Mendocino County are on a well?

About 9,991, or 29% 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 Mendocino County?

Alpha Analytical Laboratories, Inc. – Ukiah in Ukiah, about 14 miles away. Call first to ask whether they accept homeowner samples.

Do I need a permit to drill a well in Mendocino 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 Mendocino 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.