Frequently Asked Questions

What is groundwater? Where does it come from?

Groundwater is a component of the hydrologic cycle. In simple terms, water or one of its forms-water vapor and ice-can be found at the earth's surface, in the atmosphere, or beneath the earth's surface. The hydrologic cycle has no beginning or ending location; however, it is often thought of as beginning in the oceans.

Groundwater Basics
Source: California Department of Water Resources.

What is a well? How is it built?

Simply stated, a well is a hole drilled into the earth to obtain water. A slotted plastic or metal well casing is placed in the hole and a pump is installed to pump the water out.

Well Basics
Source: California Department of Water Resources.

What are the rules for constructing wells in Sonoma County?

Because improperly constructed wells, including hand-dug wells and some older wells, may allow contaminants to enter the well, laws are in place to govern the construction, modification, destruction or abandonment of wells in Sonoma County.

Permits for new wells, modifications to existing wells, or destruction of existing wells must be obtained from the Sonoma County Permit and Resource Management Department. A C-57 licensed contractor must perform work on wells in California. Be sure to check with any potential contractor to make sure they have this license.

Well and Septic Systems
Source: Sonoma County Permit and Resources Management Department

California Laws for Wells
Source: California Department of Water Resources.

What are the causes of well water contamination?

Groundwater will normally look clear and clean because the ground naturally filters out particulate matter. But, natural and human-induced chemicals can be found in groundwater.

Signs of Well Water Contamination

Contaminants Found in Groundwater
Source: U.S. Geological Survey.

Getting Up to Speed: Groundwater Contamination
Source: Environmental Protection Agency.

How do I prevent well water contamination?

Maintaining your well is essential to ensuring it is not contaminated. Routine maintenance and inspection of water wells can help protect water quality, ensure your well is operating properly, and prolong the useful life of the well system.

Well Owner Maintenance Practices
Source: National Groundwater Association.

Well Owner Website
Source: National Groundwater Association.

How do I know if my well is contaminated?

Many substances that contaminate water can be noticed without chemical testing. Below are some of the most easily observed water conditions.

Signs of Well Water Contamination

How do I test my well for water quality?

Although your water may taste and smell fine, the only way to know your water is safe is by testing it. Harmful bacteria or chemical that you cannot see, smell or taste could be present. A laboratory certified for bacteriological and/or chemical analysis can perform tests on your well water to determine its water quality.

Water Testing

How do I treat my well for bacterial contamination?

If water from a well is found to be contaminated with coliform bacteria, it may be possible to eliminate the contamination by disinfecting the well.

Well Disinfection for Bacterial Contamination

How do I treat my well for non-bacterial contamination?

Well Water Treatment for Non-bacterial Contamination

Contact Information

Public Health Division
County of Sonoma
Business Hours
Monday – Friday
8:00 AM – 4:00 PM
Office Location
625 5th Street
Santa Rosa, CA 95404
38.441823, -122.7137698

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