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County of Sonoma California

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Water Quality and Private Wells

There are many ways drinking water may become contaminated. Contamination may result from biological (bacteria, viruses, etc.) or from chemical sources. Chemical contaminations can occur from natural sources, such as arsenic leaching from rock formations, or can result from human activities, such as agricultural or industrial operations, or from improper chemical disposal at home.

Private well water is not regulated by any government agency and it is the responsibility of the individual property owner to ensure that their drinking water supply is safe by having the well water tested by a state certified laboratory. Landlords are required to provide potable water to their tenants.

Public water systems are regulated by county, state, or federal government, usually depending on the number of connections the water system serves. Public water systems are required to provide to their customers, at least once a year, a notice of water quality. While many states have adopted the safe drinking water standards of the federal government (United States Environmental Protection Agency-USEPA), the State of California has adopted its own regulatory safe water standards for public water systems that are at least as restrictive as those of the USEPA.

While the standards established for public drinking water systems are not enforceable for private well water, they can provide a parallel indication of the quality and safety of water that comes from private wells. Standards associated with public drinking water supplies are:

  • MCL is the Maximum Contamination Level permissible in public drinking water supplies. MCLs are established based on a number of considerations, including health risk, technological feasibility, treatment costs to water systems, and public hearings.
  • PHG is the Public Health Goal established for public drinking water based on health risk assessment alone and is the level at, or below which, health effects are not expected to occur from a lifetime of exposure.

Related Links

What You Need To Know About Water Quality in Your Well (pdf)
Source: Sonoma County Department of Health Services.

WELLness - A guide to Water Quality in Your Well (pdf)
Source: Sonoma County Department of Health Services.

Laboratories Certified for Bacteriological and/or Chemical Analysis (pdf)
Source: Sonoma County Department of Health Services.

Sonoma County Public Health Regional Laboratory

How to Disinfect Your Well (pdf)
Source: Sonoma County Department of Health Services.

Public Drinking Water Standards - MCLs and PHGs (MS Excel)
Source: California Department of Public Health.

CA Certified Water Treatment Devices
Source: California Department of Public Health.

GeoTracker: database of regulated contaminated sites
Source: California State Water Resources Control Board.

Agency for Toxic Substances and Disease Registry
Source: The Centers for Disease Control and Prevention.

Groundwater and Safe Drinking Water
Source: U.S. Environmental Protection Agency.

Ground Water and Drinking Water
Source: U.S. Environmental Protection Agency.

Drinking Water From Household Wells (pdf)
Source: U.S. Environmental Protection Agency.

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