1. Who will be charged?

Agricultural and commercial groundwater pumpers, and public water supply system groundwater pumpers. Rural domestic users (de minimis extractors) will not be charged directly.

2. How is groundwater use measured?

Agricultural: Consumed water estimated using a satellite-based evapotranspiration (ET) methodology that is supplemented by precipitation and land use data.

 Commercial: Water use considerations specific to the property in question are used to calculate consumptive use. Consumptive use for wineries, which make up the vast majority of commercial groundwater use, is calculated using data from the California Regional Water Quality Control Board and wine industry expertise

Public Water Supply Systems: Total pumping is converted to consumptive use based on considerations of the type of properties within a system’s service area.

 3. How are rates determined?

Based on a five-year budget projections and proportional to each user’s consumptive groundwater use. The costs associated with Services provided to each type of groundwater user are divided up by the estimated groundwater used.

4. Will the rates change over time?

Yes. In the current rate study, the rates gradually increase from year 1 to year 5 to address the potential reduction in groundwater consumption as demand reduction occurs in the basin.

5. Can I appeal my groundwater use calculation?

Yes. Users can submit a variance form and submit metered data, or other documentation if you believe your usage has been overestimated (form included on the website).

6. Why is the charge necessary and how will the funds be used?

The charge is necessary to fund the implementation of the GSP and avoid the potential for State Water Resource Control Board intervention and penalties. Funds will support groundwater monitoring, data collection, demand reduction programs, and mitigation for domestic well programs.

7.  When will the charges begin?

If successfully implemented at the August 1, 2025 public hearing, charges will be placed on the tax roll and appear on the 2025-26 property tax bill.

For more information, please see the draft cost of service study linked below.