Although your well water may taste and smell fine, the only way to know your well water is safe is by testing it.
Harmful bacteria or chemicals that you cannot see, smell, or taste could be present.

It is strongly recommended that you consult with a water treatment professional for advice about your specific
situation to ensure the water testing or water treatment you are considering will meet your needs.

The following laboratories are accredited by the Environmental
Laboratory Accreditation Program (ELAP), which means they have demonstrated capability to analyze environmental
samples using approved methods.

State Certified Laboratories for Bacteriological and/or Chemical Analysis

Disclaimer: The Sonoma County Department of Health Services makes no assumption of quality and makes no warranties
regarding providers appearing in this resource guide. This resource guide is simply a public listing provided for
consumer convenience and is not a recommendation or endorsement by the Department.

Water Quality Tests

There are many tests that can be performed on your well water to determine its water quality. This is a list of the most
commonly performed tests and their recommended testing frequencies. Because bacteria and nitrate are the most common
contaminants of well water, they should be tested more frequently. The minerals test is recommended for the purposes of
developing a baseline understanding of your water and as a way to indicate water quality changes.

Bacteria

• Test type: EPA Colilert Method, Total Coliform and Fecal Coliform
• Frequency: twice a year or after a flood or other disaster that may have impacted the well
• If the lab report shows the presence of total coliform bacteria, look for the cause, eliminate it if possible,
  and continue to test the water at an increased frequency. You may consider installing a treatment system such as
  distillation, chemical disinfection, or ultraviolet radiation.

Nitrates

• Test type: EPA Method 300 series
• Frequency: every five years
• If >45 mg/L NO3 or >10mg/L N03-N, install a treatment device or find an alternative water supply. Increase
  the testing frequency. Filtration using reverse osmosis will remove some of the nitrate.

Minerals

• Test type: EPA Method 200 series
• Frequency: every 5 years, or if a change in the water taste or color is detected
• Most water testing companies offer a group minerals test for all listed minerals. Be sure to compare the results
  with previous results.

The levels listed below are set by the California Code of Regulations, Standards for Drinking Water available at: https://www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/Lawbook.html
and https://www.waterboards.ca.gov/water_issues/programs/gama/well_owners.html.

If mineral levels are greater than or equal to these levels, you should consider installing a treatment system or
determine an alternative supply of water. An appropriate treatment system is dependent on the minerals to be removed.
Consult with a water treatment professional for more advice.

• Aluminum(AI): 020 mg/L
• Arsenic (As): 0.01 mg/L
• Barium (Ba): 1.0 mg/L
• Cadmium (Cd): 0.005 mg/L
• Chromium (Cr): 0.05 mg/L
• Fluoride(F): 2.0 mg/L
• Iron (Fe): 0.3 mg/L
• Lead (Pb): 0.015 mg/L
• Manganese (Mn): 0.05 mg/L
• Mercury (Hg): 0.002 mg/L
• Selenium (Se): 0.05 mg/L
• Silver (Ag): 0.1 mg/L

Petroleum

• Test type: Petroleum hydrocarbons by EPA Method 8015 and BTEX/MTBE by EPA Method 8260
• Frequency: every three to five years
• There is no drinking water standard for petroleum hydrocarbons. If petroleum hydrocarbons are suspected or
  detected at all, then the well should also be tested for benzene, toluene, ethylbenzene, and xylenes (BTEX) and
  methyl tert-butyl ether (MTBE), which do have standards. If petroleum hydrocarbons, BTEX, or MTBE are detected,
  then a treatment device can be used or you may consider seeking an alternative water supply.

Solvents

• Test type: Organic Compounds (solvents) by EPA Method 8260
• Frequency: every three to five years
• Each solvent has a specific drinking water standard. If solvents are detected, then a treatment device can be
  used or you may consider seeking an alternative water supply.

Pesticides

• Test type: Organochlorine Pesticides by EPA Method 8080, Herbicides by EPA Method 8150
• Frequency: every three to five years
• Each pesticide has a specific drinking water standard. If pesticides are detected, then a treatment device can
  be used, or you may consider seeking an alternative water supply.

Volatile Organic Compounds (VOCs) and Semi-Volatile Organic Compounds (SVOCs)

• Test type: Volatile Organic Compounds by EPA Method 524.2 and Semi-Volatile Organic Compounds
  by SW-845 US EPA Method 8270E.
• Frequency: after wildfire damage to water system or suspected industrial contamination
• If water pipes, well casings, or other plastic components were exposed to high heat, the water system
  was depressurized, and/ or wildfire debris entered the water system, the water should be tested for VOCs and
  SVOCs. VOCs and SVOCs may also be present in water sources impacted by industrial chemicals,
  fuel-related chemicals, pesticides, and fire retardants. Each VOC or SVOC has a specific drinking water
  standard. If VOCs or SVOCs are detected, then a treatment device can be used, or you may consider seeking an
  alternative water supply.

For more information on Drinking Water Contaminants visit https://www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/Chemicalcontaminants.html

Questions? Contact Sonoma County Environmental Health staff at (707) 565-6565 during normal working hours, 8:00 AM to
4:00 PM Monday through Friday.