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GAMA - Domestic Well - Addressing Water Quality Issues

How can I fix my well's water quality problem?

There are multiple treatment options available depending on the water quality issues identified in your private domestic well.  Examples of domestic well treatment options include filtration, reverse osmosis, distillation, and ultraviolet radiation.  Not all treatment systems treat all water quality issues. Contact your local health agency’s environmental health department for additional help in selecting a water quality professional that can help you select and install an appropriate treatment system.   

The Residential Water Treatment Device Registration program (part of the State Water Board’s Division of Drinking Water) is responsible for ensuring that residential water treatment devices sold for purifying water meet appropriate standards in the state of California. The program provides a list of registered water treatment devices for sale, current devices that reduce arsenic and nitrates, and additional information.

The Centers for Disease Control (CDC) provides a guide to drinking water treatment technologies for household use, linked below.

This guide includes information on different filtration and treatment processes, summarized below:  
Filtration Systems: Use of an absorbent medium to remove contaminants from water.
Filtration of contaminants varies greatly depending on the type of contaminant (size of particle, ionic charge of particle), the amount of contaminant present, as well as the type of filter used.

  • Microfiltration: Approximate pore size of 0.1 micron. Effective in removing sediment, protozoa, and some bacteria, not effective in removing viruses or chemicals.
  • Ultrafiltration: Approximate pore size of 0.01 micron. Effective in removing protozoa, bacteria, and some viruses, not effective in removing chemicals.
  • Nanofiltration: Approximate pore size of 0.001 micron. Very effective in removing protozoa, bacteria, and viruses. Moderately effective in removing chemicals.

Reverse Osmosis Systems: Uses a process of reversing the flow of water in a natural osmosis process, forcing water to pass through a semi-permeable membrane, removing contaminants in the process.

  • Can be very effective in removing many contaminants, such as bacteria, viruses, and many common chemical contaminants.
  • Does not remove all inorganic and organic contaminants.

Distillation Systems: Uses a process of boiling water, then collecting the resulting water vapor as it condenses, leaving many of the contaminants behind.

  • Can be very effective in removing many contaminants, such as bacteria, viruses, and many common chemical contaminants.
  • May not be effective at removing all volatile organic contaminants (VOCs), certain pesticides, and volatile solvents.

Ultraviolet Treatment Systems: Uses ultraviolet light to disinfect water or reduce the number of bacteria present.

  • Often used in conjunction with filters, by itself only effective at removing biotic contaminants, such as protozoa, bacteria, and viruses.

Water Softeners: Uses ion exchange technology to reduce the amount of hardness (calcium + magnesium) in water. They can also be designed to remove other contaminants, but do not protect against protozoa, bacteria, and viruses.

  • Effective at reducing water hardness, not effective at removing biotic contaminants, typically not effective at removing abiotic contaminants outside of calcium & magnesium.

Choosing an appropriate water filter or water treatment system for your home can be a difficult decision. The CDC has developed a guide to help you choose the water filter or treatment system that best suits your specific needs, linked below.

Removing the source of the contaminant, deepening or moving your well, linking to a public water supply, or switching to an alternative water supply (such as bottled water) are also potential options. An EPA webpage explaining how to protect your well water from potential contamination is linked below.

If you are seeking assistance with addressing a water quality issue at a domestic water well, the link below contains information about organizations that assist disadvantaged individuals and households with services for addressing water quality.

The Water Quality Association’s ‘Better Water Today’ website provides information regarding water quality issues, water treatment providers, and certified products.  


State Water Resources Control Board
Division of Water Quality
Groundwater Ambient Monitoring & Assessment Program (GAMA)
1001 I Street, 15th Floor
Sacramento, CA 95814

Telephone: (916) 341-5577
Fax: (916) 341-5463