Groundwater & Rules · Story
The Paso Robles Groundwater Basin, in Plain Numbers
The Paso Robles groundwater basin is a critically overdrafted subbasin of about 436,240 acres whose approved plan must bring pumping into balance by 2040.
By the Ranch House Water desk · Updated · 6 min read
The Paso Robles groundwater basin is the water supply for most rural homes, vineyards and ranches from San Miguel east to Shandon and south toward Creston. The state classifies it as critically overdrafted, and a local plan approved in 2023 has until 2040 to balance it. In water year 2025, total pumping was estimated at 61,400 acre-feet, close to the plan's estimate of what the basin can sustain.
What is the Paso Robles subbasin?
It is a defined groundwater basin in the state's catalog, officially the Salinas Valley – Paso Robles Area Subbasin, No. 3-004.06. The authority's 2026 fee study puts its area at about 436,240 acres, lying wholly inside San Luis Obispo County and taking in the City of Paso Robles plus Shandon, San Miguel, Creston, Cholame and Whitley Gardens.
The state calls a basin critically overdrafted when continuing current practices would probably cause significant harm to the environment, the economy or communities. In the authority's plainer words, more water is pumped out than is naturally replenished.
Who manages the basin?
Under the Sustainable Groundwater Management Act (SGMA), local groundwater sustainability agencies run the basin and answer to the Department of Water Resources. On March 14, 2025, four of them formed the Paso Robles Area Groundwater Authority: the County of San Luis Obispo, the City of Paso Robles, the Estrella-El Pomar-Creston Water District and the Shandon-San Juan Water District. The San Miguel Community Services District agency did not join. Which agency covers a parcel depends on where it sits, and the authority points owners to the county's map viewer and their parcel number.
How did the state review the plan?
The plan has passed through five dated stages, each with a date on the public record.
| Date | What happened | Source |
|---|---|---|
| January 30, 2020 | Local agencies submitted the groundwater sustainability plan | DWR SGMA portal |
| January 21, 2022 | DWR found the plan "Incomplete" | DWR determination letter |
| 2022 (dated June 13, 2022) | Revised plan submitted | Groundwater authority |
| June 20, 2023 | DWR approved the revised plan | WY2025 Annual Report |
| January 30, 2025 | Five-year periodic evaluation prepared; DWR status "Under Periodic Review" | DWR SGMA portal |
The 2022 finding matters to anyone on a household well. DWR said the first plan did not explain how it weighed the dewatering of domestic wells as levels fell. Its original minimum thresholds were set 30 feet below 2017 levels at every monitoring site. When DWR approved the revision in 2023, it recommended that the agencies consider ways to address drinking-water impacts during the years before the basin reaches balance.
The basin is not on state probation. The State Water Board's SGMA page lists state intervention only for the Tulare Lake and Tule subbasins, and probation can follow only a finding that a plan is inadequate, which Paso Robles has never received. As of October 30, 2026, DWR shows the plan as "Under Periodic Review," with no decision posted on the 2025 evaluation.
How much water is pumped?
Pumping rises and falls with rain and crop demand. The basin's latest annual report, covering water year 2025 and issued March 26, 2026, estimates total extraction at 78,000 acre-feet in 2020, 80,700 in 2021, 82,700 in 2022, 63,600 in 2023, 75,100 in 2024 and 61,400 in 2025. The plan's long-term sustainable yield is 61,100 acre-feet a year. Irrigated agriculture made up 91 percent of the 2025 total.
- 202078,000 acre-feet
- 202180,700 acre-feet
- 202282,700 acre-feet
- 202363,600 acre-feet
- 202475,100 acre-feet
- 202561,400 acre-feet
Source: WY2025 Annual Report
Read the 2025 figure with care. The report says the drop came from a change in how farm water demand is estimated and is not an actual reduction of roughly 15,000 acre-feet. Pumping close to the sustainable yield in one year does not mean the basin is balanced.
What are water levels doing?
Hydrographs for many monitoring sites trace a downward trend that began in the late 1990s, though some have held fairly steady. Levels in 2025 were generally similar to the year before. Of 22 representative wells in the main aquifer, 3 were below their minimum threshold in 2025, and the report counts each of those as an undesirable result under the plan. One of them has been below its threshold for six years running.
The report also notes that several dry wells were reported or replaced during the year, which it calls a direct result of declining levels. It names communities and rural homes that rely only on groundwater as the users of most concern. Land sinking has been small, at most 0.20 feet between June 2020 and June 2025, and water quality shows no significant change since 2015.
Is there any new water coming?
Not soon, by the report's own account. It states that no feasible project has yet been identified that would materially help the basin meet its goals, and that no surface water is currently available for farm use or recharge within the subbasin. The City of Paso Robles draws on Nacimiento Lake water and river wells, and Shandon can receive State Water Project water, but rural wells depend on the aquifer.
That leaves pumping limits, fees and land-use rules as the main tools. The authority's 2025 attempt to set a fee failed after a majority protest. Its second try succeeded, as our brief on the groundwater fee and household wells explains. Household pumpers are treated separately, covered in household wells and the basin rules, and the county's own limits are in county rules for new wells and building.
Where to call
- Paso Robles Area Groundwater Authority — questions on the basin plan, annual reports and the per-acre-foot fee. pasoroblesaga.org
- County of San Luis Obispo, Groundwater Sustainability — what the county's own groundwater agency area includes. County groundwater page
- California Department of Water Resources, SGMA Portal — the plan text, its review status and every annual report. SGMA Portal
- San Miguel Community Services District — parcels inside the district's separate groundwater agency area. District site
Common questions
Is the Paso Robles basin on state probation?
No. DWR found the first plan incomplete in 2022 and approved a revised plan in 2023. The State Water Board lists only the Tulare Lake and Tule subbasins for intervention.
Why did pumping fall so much in 2025?
Mostly because the method for estimating farm water use changed. The annual report says the lower figure is not an actual 15,000 acre-foot reduction in pumping.
How far have water levels dropped near my house?
No single figure is published for the whole basin. The annual report shows hydrographs for monitoring wells; the authority can point you to the one nearest your parcel.
Does San Miguel belong to the groundwater authority?
The San Miguel Community Services District's agency did not join when the authority formed in March 2025. Ask the district or the authority how its area is managed today.
Where can I read the plan itself?
The DWR SGMA Portal holds the plan, the state's determination letters and the annual reports for water years 2019 through 2025.
Sources
- DWR SGMA Portal — Paso Robles Area Subbasin plan record and determinations — basin name and number, 2020 submittal, 2022 "Incomplete" finding and its reasons
- Paso Robles Subbasin Water Year 2025 Annual Report, March 26, 2026 — 2023 approval, pumping by year, sustainable yield, water levels, dry wells, subsidence, supply projects
- Paso Robles Area Groundwater Authority — Rate and Fee Study, May 2026 — basin area and communities
- Paso Robles Area Groundwater Authority — Member Agencies — members and how to find your agency
- Paso Robles Area Groundwater Authority — press release, February 27, 2026 — critical overdraft, 2040 deadline
- Paso Robles Area Groundwater Authority — Groundwater Sustainability Plan — revised plan dated June 13, 2022
- DWR — Critically Overdrafted Basins (archived copy, September 2026) — definition of critical overdraft
- State Water Resources Control Board — SGMA — basins under state intervention
- Paso Robles Area Groundwater Authority — August 1, 2025 hearing update — the 2025 fee protest