San Elijo/San Dieguito Valley Groundwater Project


San Diego county relies heavily on imported water from far-off places like the Sacramento-San Joaquin Bay-Delta and Colorado River to serve its customers.

As imported water costs have continued to rise and the availability of that water has become more uncertain, Olivenhain Municipal Water District started exploring development of local, sustainable water sources to diversity its water portfolio, such as recycled water and desalination.

One potential source of sustainable water development is local groundwater. This method would extract brackish groundwater from a nearby basin, treat it via reverse osmosis to potable standards, and deliver it to customers for uses like drinking water and fire protection.

Potential Project Sites

OMWD has been exploring the feasibility of brackish groundwater desalination in the San Elijo and San Dieguito Valleys.

Data gathering in the San Elijo Valley has been underway since 2012. So far, studies indicate that this area has the potential to support one to two million gallons per day of brackish groundwater desalination, which could supply up to five percent of OMWD’s potable water demand.

The San Dieguito Valley brackish groundwater desalination feasibility study began in the fall of 2016. The study examined a variety of factors to determine whether a brackish groundwater desalination project is possible in the area.

On December 12, 2018, OMWD’s Board of Directors adopted a mitigated negative declaration as part of the environmental review process for this potential project. A pilot test well was constructed in April 2019 and a pump test is underway to verify the water balance of the groundwater basin, potential impacts on current wells in the area, and water treatment technologies.  

OMWD may opt to pursue a brackish groundwater desalination project in either the San Dieguito Valley or the San Elijo Valley. That decision will likely be based on several criteria including determining which area can provide the most cost-efficient and environmentally responsible water yields without impacting existing users.

Map of San Elijo and San Dieguito Valleys


Since the brackish groundwater desalination project was conceived in 2010, it has garnered more than $1,500,000 in grant funds from the United States Bureau of Reclamation and the California Department of Water Resources. OMWD continues to seek grants to support the study of the potential project.

Project Support

The exploration of these two projects has been supported by several local, state, and federal agencies including the City of Encinitas, City of Solana Beach, County of San Diego Department of Parks and Recreation, San Elijo Joint Powers Authority, San Elijo Lagoon Conservancy, United States Geological Survey, California Department of Water Resources, and United States Bureau of Reclamation.

For More Information

Please see the individual project pages linked above for more information, or contact Joey Randall, OMWD Assistant General Manager, at 760-753-6466.