The Los Osos Groundwater Basin—the community’s only source of drinking water—continues to face long-standing challenges from over-pumping, seawater intrusion and legacy nitrate contamination, according to the Los Osos Community Services District’s latest water report.
The annual report, reviewed by the district this week, shows that water production has steadily declined since 2015 and remained relatively stable since 2019, even through years of drought and above-average rainfall. General Manager Ron Munds credited much of that progress to conservation efforts by local residents.
“Water use is down, but we’re still seeing signs of seawater intrusion slowly creeping in,” Munds said. “There’s still more to do. We’re also looking at bringing in imported state water to help offset pumping and help the basin recover.”
The upper part of the basin, or upper aquifer, has been polluted with nitrates after decades of septic tank use before the community connected to a sewer system. Most domestic water pumping now comes from the lower aquifer, which has experienced increasing levels of seawater intrusion due to overuse.
To address that, the district is finishing a new groundwater well that will shift pumping away from the western side of the basin, where intrusion is most severe, toward safer eastern areas. The well is expected to be operational by July.
The district is also pursuing the Water Supply Resiliency Project, which would connect Los Osos to the State Water Pipeline in the Chorro Valley. The project was included in a federal water infrastructure bill but still awaits final approval and funding from the U.S. Army Corps of Engineers.
Munds said a study outlining long-term water supply solutions and associated costs is expected to be released for public review in August or September.
