California county well guide

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

About 1,373 households in Colusa County, 16% of the county, rely on a private well. Nobody tests that water unless the owner does.

Labs within 40 milesLicensed contractors
16%of households on a private well
Share on wells, county vs state
Colusa County16%
California average4%
11licensed contractors serve the county
40+ mito a certified lab; mail-in kits recommended
Nostatewide test required when a home is sold

About one in 6 households in Colusa County relies on a private well, around 1,373 homes. Outside the towns with public water, wells are the norm here.

Local rules for wells in Colusa County

The rules that apply in Colusa 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 Colusa County

Colusa County has no certified lab within 40 miles, so most owners here test by mail. Order bottles from a certified lab, sample from the cold tap before any treatment, and ship the same day with an ice pack.

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Licensed well contractors serving Colusa County

Licensed help in Colusa County includes Big’n & Son Drilling Inc and Cherry Glenn Drilling and 9 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 Colusa County follow the rock underneath it. Typical wells here run 150 to 310 feet; the median of 434 domestic wells reported to DWR since 2000 is 210 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

150 to 310 feet; the median of 434 domestic wells reported to DWR since 2000 is 210 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: Sutter County, Yuba County, Glenn County, Lake County.

What well work costs in Colusa 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 Colusa County well owners ask

How many homes in Colusa County are on a well?

About 1,373, or 16% 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 Colusa County?

There is no certified lab within 40 miles. Use a mail-in kit from a California certified lab, or the county health department if it collects samples.

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