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California

How deep are the wells, county by county.

Every well drilled in California for water supply has a completion report on file with the state. That is 478,261 of them, and this is what they say — the middle county finishes at 220 ft, and 54 of 55 counties have been finishing deeper decade after decade.

The shape of the record

  • Counties drilling deeper

    54 of 55

    Comparing each county's first and last decade with enough reports to take a median. 1 held steady, 0 came up. Completion depth follows where and why people drill as much as it follows a water table, so this counts filings rather than explaining them.

  • Steepest change

    3.4×

    Alameda County: a median of 87 ft in the 1970s against 300 ft in the 2020s.

  • Deepest counties

    Madera, 400 ft

    Madera 400 ft · Kern 400 ft · San Diego 398 ft · Santa Barbara 390 ft · Los Angeles 372 ft

  • Shallowest counties

    Del Norte, 42 ft

    Del Norte 42 ft · Humboldt 100 ft · Sutter 117 ft · Lake 125 ft · Mendocino 140 ft

  • Most drilled

    Fresno, 34,423 wells

    Fresno 34,423 · Sonoma 25,866 · Riverside 20,857 · Nevada 19,782 · Tulare 19,110

All 55 counties

Sorted by how much of the record each county holds. Every page carries that county’s depths, the water level and yield where drillers recorded them, how the median moved decade by decade, and what none of it can tell you.

Counties the record covers thinly

Fewer than 500 filed reports. The counts are real; a median drawn from them would not be worth printing, so these get a line rather than a page.

Imperial (255) · Alpine (231) · null (204) · San Francisco (32)

How these numbers were counted

  • Source

    California Department of Water Resources

    Well Completion Reports. California public record; CNRA open data. Read 2026-09-07. The state publishes the reports; the aggregation is ours, and it is rebuilt from scratch rather than edited.

  • Counted

    newly drilled wells reported for water supply

    The same filter the analysis engine applies to Californian ground, repeated verbatim, so a county page and a survey are counting the same wells.

  • Depth

    Total completed depth

    total completed depth in feet, as the driller reported it. Medians and percentiles are exact — taken from the ordered record, not estimated from an average.

  • Level and yield

    Only where filed

    the static water level recorded when the well was finished, in feet below ground; the yield the driller measured at the time of the test, in gallons per minute. Both live in text columns upstream, so both carry their own count on every page — always smaller than the well count, and printing the median without it would quote an unknown fraction of the record as if it were all of it.

  • Bar

    500 reports

    For a page. A decade needs 30 before it is given a median; below that it is reported as a count.

Common questions

How deep is the average water well in California?
Across the 55 California counties with at least 500 filed completion reports, the middle county's median well is 220 feet deep. County medians run from 42 feet in Del Norte County to 400 feet in Madera County, so a single statewide number describes almost nobody.
Are California wells getting deeper?
On the filed record, in nearly every county. Comparing each county's first and last decade with enough reports to take a median, 54 of 55 counties have gone measurably deeper, 1 held steady and 0 came up. The same test run on Texas returns a very different answer, which is a useful reminder that this is a description of what was filed rather than an explanation of what is underground.
Do these pages tell me the depth to water?
They tell you what drillers wrote down, which is not the same thing. California's reports carry a static water level measured on the day the well was finished — some of those days were forty years ago. Those readings describe the wells they came from. They are not a current water table, and no average of old filings becomes one.
Where does this data come from?
The California Department of Water Resources's Well Completion Reports. These pages count newly drilled wells reported for water supply — 478,261 of them — and take medians from the ordered record rather than estimating from an average. Read 2026-09-07.

A county is not a parcel

These medians describe whole counties. Beneath answers the narrower question: draw a boundary, and it scores the ground inside it against geology, well records, terrain, aquifers and satellite evidence, then ranks which ground is worth investigating and which to rule out — with the records behind every conclusion and a stated confidence for how much of it to believe.

See how it works · Other states