Phone: (707) 823-3191 Fax: (707) 317-0057

Certified Testing For Residential Building Permits

Sonoma County water well yield tests – For residential building construction permits.

For some new construction a water yield certification report may be required as a building permit condition. Sonoma County is differentiated into 4 water groundwater availability zones. Zones 3 and 4 require a certification of water yield also known as a well yield report. Click HERE to download the groundwater availability map. Alternatively, we can look up the parcel using the Sonoma County Activemap and click the groundwater availability overlay button.

Testing Time restriction:

July 15th through October 1st or as extended by the Project Review and Advisory Committee (PRAC). Shallow wells (wells less than 50 feet) and spring testing time line may not be extended.

Water yield requirement:

1 Gallon Per Minute per dwelling unit.

Test length requirement:

1 to 2 connections: 8 to 12 hours

3 to 4 connections: 16 to 24 hours

5 or more connections: 48 to 72 hours

Water level recovery requirement:

Water level must recover to within 90% of the total draw down within 72 hours after completion of the yield test.





Napa County water well yield tests – For residential building construction permits.

Testing time restriction:

Can be performed any month of the year.

Water yield requirement:

Napa County requires the well to have a minimum sustained yield of at least 1 Gallon Per Minute per dwelling unit.

Test length requirement:

Wells producing less than 5 gallons per minute are required to be tested for at least 4 hours. Wells producing 5 gallons per minute or greater are required to have a stabilized yield for a minimum of 1 hour.

Water level recovery requirement:

None