California domestic well testing: State Water Board guidance and ELAP labs
Short answer: The California State Water Board recommends testing a domestic well's water quality every year and comparing results to drinking water limits. It suggests an ELAP-accredited lab, which supplies bottles and can help with sampling. Basic sampling can cost $100 to $400, so ask for a written estimate first.
The U.S. Geological Survey estimated that about 1.44 million people in California supplied their own household water in 2015. USGS says the most common source of self-supplied water is a well. [source] [source]
Test every year
The State Water Board's GAMA program recommends testing domestic well water quality every year. If results are high, compare them to the Maximum Contaminant Levels set for public water systems. MCLs aren't enforceable for domestic wells, but the Board recommends you observe the same levels. [source]
What to test for
The Board lists bacteria (such as E. coli and total coliforms), inorganics (such as arsenic, uranium and total dissolved solids), fertilizers such as nitrate, pesticides, and industrial solvents. [source]
Where to test and cost
The Board suggests an Environmental Laboratory Accreditation Program (ELAP) lab. The lab supplies sampling bottles and can help you sample. Basic sampling can cost $100 to $400, so ask for a written estimate first. [source] Find labs on the California ELAP certified laboratories map. [source]
Renting out a home with a well (AB 2454)
If a domestic well serves a rental property inside the area of a free testing program funded or regulated by the State or a Regional Water Board, the owner must test through that free program and share results with tenants within 10 days. The owner can't charge tenants for testing. [source]
County guides
No county pages for this state yet. Your local health department is the first stop, per EPA guidance. [source]
FAQ
How often should California domestic well owners test their water?
The California State Water Board recommends testing a domestic well's water quality every year and comparing results to drinking water limits. It suggests an ELAP-accredited lab, which supplies bottles and can help with sampling. Basic sampling can cost $100 to $400, so ask for a written estimate first.
How much does well water testing cost in California?
The State Water Board says basic sampling can cost $100 to $400 and recommends asking for a written estimate before sampling.
Sources
- USGS – Estimated Use of Water in the United States, County-Level Data for 2015 (domestic self-supplied population) (accessed 2026-10-23)
- USGS – Domestic Water Use (accessed 2026-10-23)
- California State Water Board – GAMA Domestic Well Testing (accessed 2026-10-23)
- California ELAP Certified Laboratories GIS Map (accessed 2026-10-23)
- California State Water Board – Rental Property Domestic Well Testing Requirements (AB 2454) (accessed 2026-10-23)
- US EPA – Protect Your Home's Water (accessed 2026-10-23)
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