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Last Edited: 9/8/2011

Private Wells

According to the U.S. Geological Survey (USGS), as many as 3,812,470 people in California were served by domestic (self-supplied) wells in 2000. Because private water wells in the country are generally not regulated by federal or state standards, it is up to the owners' discretion to conduct regular testing and clean-up of their wells.

A USGS study conducted from 1991 to 2004, titled “The Quality of Our Nation’s Water: Quality of Water from Domestic Wells in Principal Aquifers of the United States,” sampled 2,100 private wells in the country and found at least one contaminant in more than 20 % of them. According to this study, the contaminants found in wells vary across the country, frequently following geographic patterns. Although this study was not a comprehensive risk and toxicity assessment, it does point out the importance of regularly testing private water wells for contaminants that compromise the quality of drinking water and may cause health problems for consumers.

In June 2009, the American Academy of Pediatrics (AAP) published a policy statement providing recommendations for inspection, testing, and clean-up of wells that provide drinking water for children and for pregnant and breastfeeding women. In this publication, the AAP recommends that wells be tested once a year for coliform bacteria and nitrates, and that they be tested more than once per year if:

  • someone in the household is pregnant or nursing;
  • there are unexplained illnesses in the household;
  • neighbors find a dangerous contaminant in their well water;
  • there is a change in the odor or taste of the well water;
  • there is a chemical spill in proximity to the well or there has been a significant repair to or replacement in the well;
  • there is an infant or child younger than one year in the household and the yearly test indicates a fluctuation in nitrate concentration or the testing did not include nitrates; or
  • there is damage or disturbance to the well.

 Resources for private well owners

  • “A Guide for the Private Well Owner” is a comprehensive guide originally developed by Santa Clara County and adopted by other counties. This guide includes a list of well owner responsibilities, information on well construction and maintenance, water quality protection, sampling and treatment, and an additional resource guide. The electronic link to this fact sheet can be found at:

  • “What You Need To Know About Water Quality In Your Well” is a trifold fact sheet originally developed by Sonoma County. This fact sheet explains the basics about private wells, provides an explanation about how wells can become contaminated, encourages private well owners to know their surroundings and test their wells, suggests what to test for and how to protect private well water, and lists local resources. The electronic link to this fact sheet can be found at: 

 Useful links

  • State Water Resources Control Board:     (follow link on page to “Sampling My Private Well”)





Related Projects

  • Private Water Well Statewide Outreach  -- The California Department of Public Health (CDPH) is conducting a statewide outreach to provide information on private wells and health....