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California groundwater basins and SGMA priority

For land that will rely on a well, the groundwater basin matters. This guide explains California’s basin priorities under the Sustainable Groundwater Management Act (SGMA), what “critically overdrafted” means, and how to see which basin a location is in.

Data as of October 23, 2026; refreshed monthly.

In short

Screening only — not a legal or official determination. Verify with the issuing agency.

What basin priority means

DWR classifies each of California’s 515 groundwater basins into one of four categories: high, medium, low or very low priority. A basin’s priority decides which parts of SGMA apply. In high- and medium-priority basins, local groundwater sustainability agencies (GSAs) must form, adopt groundwater sustainability plans (GSPs) and manage groundwater for long-term sustainability.

DWR completed its latest prioritization, SGMA 2019 Basin Prioritization, in December 2019, and says no new prioritization is planned at this time.

Critically overdrafted basins

SGMA directs DWR to identify basins in critical overdraft: basins where continuing current water management would probably cause significant overdraft-related environmental, social or economic harm. These basins had the earliest deadline to adopt sustainability plans. If a basin’s plan falls short, the State Water Resources Control Board can step in.

Why it matters for land and wells

Well permits come from the county, and a basin’s groundwater sustainability agency can add its own requirements, which can include metering, reporting or fees. In critically overdrafted basins, new wells can face extra review or limits. Ask both the county and the local GSA before counting on a new well.

How to check a location on Outpost

  1. Look up the parcel’s address on the map, or click anywhere in California.
  2. The scorecard’s groundwater row shows the basin’s name and priority, and flags critically overdrafted basins.
  3. “Not in Designated Basin” means the point is outside DWR’s mapped basins. It doesn’t mean there is no groundwater.
  4. To see the basins, turn on the Groundwater Basins layer. Its parts (Critically Overdrafted, High Priority, Medium Priority, and Low & Very Low) can be switched on and off separately.

Groundwater basin colors on the map:

What Outpost can’t tell you

Open the mapFree, no account. Search an address or click any point in California.

Common questions

What does a high-priority basin mean?

DWR ranked the basin high under SGMA, so it must be managed by local groundwater sustainability agencies under a groundwater sustainability plan.

What is a critically overdrafted basin?

A basin DWR has identified where continuing current water management would probably cause significant overdraft-related harm. These basins had the earliest deadline for sustainability plans.

Can I drill a well there?

It depends on the county’s well permit rules and the local groundwater sustainability agency. Ask both before buying land that will rely on a new well.

My land isn’t in a mapped basin. Can I still have a well?

Possibly. Outside DWR’s mapped basins, groundwater can still exist, and county well permits still apply. Outpost’s groundwater row only reports DWR’s basin map.

Official sources