Water Quality

The San Diego County Water Authority is the water wholesaler to 24 member agencies and serves approximately 90 percent of the county’s water needs through a diversified water portfolio. The Water Authority receives both treated and untreated water from the Metropolitan Water District (MWD). This water originates from the Colorado River and from Bay-Delta area of northern California.


Untreated water must be treated prior to use by the public. One of the treatment plants, the Twin Oaks Valley Water Treatment Plant, located within the county is owned by the Water Authority. This plant utilizes the latest technology to produce up to 100 million gallons of potable water each day.

Water goes through the treatment process at the Twin Oaks Valley Water Treatment Plant.

In addition to the Water Authority, other agencies that own and operate treatment plants within the county include:

•    Escondido (City of) - joint ownership with Vista Irrigation District
•    Helix Water District
•    Oceanside (City of)
•    Olivenhain Municipal Water District
•    Poway (City of)
•    San Diego (City of)
•    Santa Fe Irrigation District - joint ownership with San Dieguito Water District
•    Sweetwater Authority (operating for South Bay Irrigation District and National City)

Treated water is purchased by the Water Authority from the Metropolitan Water District, the Helix Water District, the Olivenhain Municipal Water District and the cities of Oceanside, San Diego, and Poway. Treated water sources can be delivered directly into member agency’s distribution systems for customer use. Whether the water is treated by MWD, the Water Authority, or a local agency, all treated water served in San Diego County meets or exceeds rigorous state and federal water quality regulations.

Additional Information:

For additional information on fluoridation, click here.
For additional information on lead testing, click here.


Metropolitan Water District: links on water quality
California Department of Health Services (DHS)