California Well Water
Last reviewed October 29, 2026
Overview
Private wells supply water to many California households. Because they are generally not regulated like public systems under the federal Safe Drinking Water Act, testing and wellhead protection are the owner’s responsibility.
Hydrogeology & what it means
California pumps from the Central Valley aquifer system and numerous coastal and inland basins. The documented regional concerns below indicate what is worth testing for — not what any individual well contains.
Documented regional concerns
- Nitrate from agricultural and septic influence, especially in farmed areas.
- Naturally occurring arsenic in parts of the state — odorless and tasteless, so only testing reveals it.
- Naturally occurring uranium in some aquifers.
- Hexavalent chromium documented in some groundwater.
- Saltwater intrusion and elevated chloride/sodium in coastal or over-pumped areas.
- Hard water from carbonate (limestone/dolomite) aquifers.
These are documented possibilities, not a reading of your well
Frequently asked questions
What should well owners in California test for?
A practical panel for California private wells includes Total coliform bacteria, Nitrate (as N), pH, Arsenic, Uranium, Chromium (total and hexavalent), Chloride, Total dissolved solids, Total hardness. Test bacteria and nitrate at least annually and use a state-certified laboratory; confirm local recommendations with your state health department and University of California (UC ANR) Cooperative Extension.
Are private wells regulated in California?
Private wells are generally not covered by the federal Safe Drinking Water Act, though California or local rules may apply to construction, permitting, or testing. Public-system limits such as EPA MCLs are useful reference points, not automatic legal limits for your well.