Water Quality

A malfunction at the Twin Oaks Valley Water Treatment Plant on April 21-22, 2019, resulted in a citation from the state Division of Drinking Water. The water in regional pipelines continued to be safe for all uses due to additional treatment processes that are in place.

The Water Authority has set up a hotline at (858) 284-4142 to address questions from the public about the April 21-22 incident. 

Para más información, por favor comuníquese con la Water Authority al (858) 284-4142. 

Click here to see if your home was in the affected service area.

Haga clic aquí para saber si su hogar ha sido afectado.

Click here for answers to Frequently Asked Questions. 

Haga clic aquí para obtener preguntas y respuestas frecuentes.

Click here for the Tier 2 Public Notice. 

Haga clic aquí para obtener el aviso público de nivel 2. 

Click here for the public notice.

Haga clic aquí para obtener el aviso público. 

If there had been an actual water quality emergency, the public would have been notified immediately. After the citation was issued on June 4, the Water Authority worked closely with impacted member agencies to follow state-manded noticing requirements. That process involved identifying and notifying all customers who may have received water from the Twin Oaks plant during the April 21-22 incident. Affected agencies are Carlsbad Municipal Water District, Helix Water District, City of Oceanside, Otay Water District, Padre Dam Municipal Water District, Rainbow Municipal Water District, Ramona Municipal Water District, Rincon del Diablo Municipal Water District, Vista Irrigation District, City of San Diego, Vallecitos Water District and Valley Center Municipal Water District.

To learn more about the water treatment process, click here

The malfunction lasted for about 15 hours, when ozone dosage levels in the plant fell below state-mandated levels because a valve failed to fully open. Ozone is a common disinfectant used in water treatment systems to kill bacteria and other organisms. To be effective, water must be in contact with the proper dosage of ozone for specific amounts of time.

To learn more about the Twin Oaks Valley Water Treatment Plant, click here

CH2M Hill/Jacobs operates the Twin Oaks plant under a contract with the Water Authority, but the citation was issued to the Water Authority as the plant owner and permit holder. The citation was the first at the Twin Oaks plant in more than a decade of service.

Corrective actions were taken immediately, and the lapse was reported to state regulators. The contractor has updated its operational procedures and installed additional monitoring equipment to prevent similar problems in the future.

Water quality overview

Potable water supplied by the Water Authority to its member agencies comes from three primary sources: the Claude "Bud" Lewis Carlsbad Desalination Plant, the Robert A. Skinner Water Treatment Plant in Riverside County -- owned and operated by the Metropolitan Water District of Southern California -- and the Twin Oaks Valley Water Treatment Plant north of San Marcos.

Here are the 2018 test results for each facility:

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

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 standards.

Additional Information:

For additional information on fluoridation, click here.

For additional information on lead testing, click here.


Metropolitan Water District: water quality

California State Water Resources Control Board - Division of Drinking Water