If you grow grapes in the Napa Valley — or just own a house out in the country with a well — a new charge is about to show up on your property tax bill. Napa County set the fee six months ago. It’s only now getting around to explaining it.
The county’s Groundwater Sustainability Agency adopted what it calls a Groundwater Sustainability Fee back in December 2025, and the first bills land in the 2026-27 budget year, split across the December 2026 and April 2027 property tax statements. It applies to one place only: land sitting over the Napa Valley Subbasin, the groundwater basin under the valley floor.
Key takeaways
- Napa County’s new Groundwater Sustainability Fee starts in the 2026-27 budget year, billed on the December 2026 and April 2027 property tax statements.
- It applies only to property over the Napa Valley Subbasin: growers, rural well owners and public water systems.
- Growers pay up to $98.74 per planted acre; rural well owners pay a flat $62.58 per parcel; public water systems pay $129.87 per acre-foot.
- The fee isn’t metered — growers are billed by the acre (the county assumes 90% is groundwater-irrigated unless documented), homeowners by the parcel.
- Two virtual community meetings: June 17 (3-4:30 p.m.) and July 1 (5:30-7 p.m.). Deadline to contest your parcel’s records or subbasin status: July 10, 2026.
- The Groundwater Technical Advisory Group takes up pumping-reduction incentives today, June 11, at 1:30 p.m. in the Board of Supervisors chambers; it meets again Sept. 10.
Who pays, and how much
Growers get billed by the acre. The base rate is $38.58 a year for every planted acre, plus another $60.16 for every acre watered from a well — $98.74 an acre all in if you irrigate with groundwater. And the county assumes you do: it figures 90% of your planted acreage is groundwater-irrigated unless you hand over paperwork showing you dry farm or pull water from somewhere else.
Rural homeowners on a well pay a flat $62.58 per parcel, no matter how much they pump. The cities and other public water systems get billed by volume — $129.87 for every acre-foot they take out of the ground.
Why there’s a fee at all
The short version is a state law called the Sustainable Groundwater Management Act, which orders local agencies to get their basins to sustainable pumping levels by 2042. Napa’s problem is on the record. In the 2025 water year the valley pulled about 16,580 acre-feet out of the subbasin — past the 15,000 acre-feet the county considers sustainable, and roughly 40% of all the water used here. Average it over the last seven years and the number climbs to 17,700 acre-feet. The county’s own plan calls for cutting use 10%.
The fee doesn’t buy anyone water. It pays for the monitoring, reporting, planning and paperwork the state requires — proof, on file, that the county is managing the basin.
Growers are already doing the math
The pushback started before the first bill. On the Napa Valley Grapegrowers Association’s explainer, one grower ran the numbers and pegged the cost at about $650 an acre-foot, then asked why a program built around saving water doesn’t reward anyone for using less. Another wanted to know whether vineyards watered from a retention pond get hit with the irrigation charge anyway.
That gap — a fee now, incentives maybe later — is exactly what the county is wrestling with, and it’s on the table today. The Groundwater Technical Advisory Group meets at 1:30 p.m. June 11 in the Board of Supervisors chambers at 1195 Third St. in Napa to talk through pumping-reduction incentives, a voluntary certification program and a concept for paying growers to hold off on replanting pulled vines so the ground can recharge. The group meets again Sept. 10 at the same time and place.
One catch: for most people this isn’t a bill for what you actually pumped. The county says there isn’t enough well-meter data to charge by use, so growers are billed by the acre and homeowners by the parcel, on the county’s assumptions. If those assumptions are wrong for your land — you dry farm, you water from a pond — you have to document it or appeal after the bill arrives.
What to do before the bill shows up
The county is holding two virtual meetings to walk people through it — June 17 from 3 to 4:30 p.m. and July 1 from 5:30 to 7 p.m., both on Zoom. And if you think your parcel isn’t actually over the subbasin, or the county’s records about your property are wrong, you have until July 10 to say so and get it reviewed.
The fee is here either way. The carrots for using less water are still being drawn up — which is the part growers will be watching when the advisory group meets today.
Frequently asked questions
Who has to pay the Napa groundwater fee?
Owners of property over the Napa Valley Subbasin — agricultural growers, self-supplied users including most domestic well owners, and public water systems. Property outside the subbasin is not charged.
How much is the fee?
Growers pay $38.58 per planted acre plus $60.16 per groundwater-irrigated acre, up to $98.74 per acre. Rural well owners pay a flat $62.58 per parcel per year. Public water systems pay $129.87 per acre-foot.
When will I be billed?
The fee takes effect in fiscal year 2026-27. Growers and rural residents will see it on their December 2026 and April 2027 property tax bills. Public water systems are billed separately starting in fall 2026.
What if I dry farm or my well is outside the subbasin?
The county assumes 90% of planted acreage is groundwater-irrigated unless you submit documentation of dry farming or an alternative water source. If you believe your parcel is outside the subbasin or your records are wrong, contact the county by July 10, 2026.
Why is Napa charging this fee?
The state’s Sustainable Groundwater Management Act requires the county to bring the Napa Valley Subbasin to sustainable pumping by 2042. The fee funds groundwater monitoring, reporting, planning, administration and compliance — not the water itself.