San Mateo County, CA Water Table Trend
Is the water table dropping in San Mateo County, CA?
Over 29 years of USGS readings, the well tracking San Mateo County's aquifer is declining, slower than most declining counties: 0.9 ft per decade.
This is one representative well, not a county-wide survey, the same grain limit every page here discloses.
San Mateo County's source well, in detail
Depth to water at the last reading was 39.6 ft below land surface. Readings span 1993-05-26 to 2022-04-20, 35 measurements from USGS well USGS-372750122112201 (005s003w28r003m), part of the National Water Information System. The qualifying bar and the OLS fit behind this trend are documented in the methodology guide.
How San Mateo County compares nationally
San Mateo County sits at rank 1052nd of 1,449 ranked counties, ordered rising-to-declining, so a low number means a rising water table and a high one means fast decline. San Mateo County, California is home to about 742,893 people. See the fastest-moving counties guide for how San Mateo County stacks up against the most extreme cases nationally.
If you own a well in San Mateo County
A dropping water table means a residential pump has to reach deeper and work harder, which shortens its life. In San Mateo County, that trend is real, not assumed: 0.9 ft per decade over 29 years.
Depth and quality are separate questions
This page answers a depth question, not a quality one. A well in San Mateo County can be stable in depth and still worth testing for quality, or declining and still test clean, the two are measured separately, and only a direct test settles the second one.