aerial view of water cleaning facility

Safe Water Delivery

The delivery of safe water to the Water Authority’s 23 member agencies and their customers is the top priority for the Water Authority. Regular water quality monitoring and the use of online monitoring equipment ensure that the Water Authority is delivering high-quality, safe water to its member agencies 24 hours a day, seven days a week.


Regional Treatment Facilities

Potable water supplied by the Water Authority to its member agencies comes from three primary sources. 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.

Claude “Bud” Lewis Carlsbad Desalination Plant

The Carlsbad Desalination Plant is the nation’s largest, most environmentally-friendly and most technologically advanced seawater desalination plant. It is the result of a public-private partnership between the Water Authority and Poseidon Water, and it treats up to 50 million gallons per day.

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Robert A. Skinner Water Treatment Plant

The Robert A. Skinner Treatment Plant is owned and operated by the Metropolitan Water District of Southern California in southwest Riverside County. The plant provides treated water to residents in Riverside and San Diego County counties. It treats water from the Colorado River Aqueduct and the State Water Project, with a capacity of 350 million gallons a day.

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Twin Oaks Valley Water Treatment Plant

This water treatment plant is located north of San Marcos.

This submerged membrane water treatment plant provides high-quality drinking water for San Diego County. Located next to the Water Authority’s aqueduct in a semirural area north of San Marcos, the high-capacity treatment plant can provide enough water to serve up
to 220,000 households per year.

linkWebpage download this documentWater Quality Report download this documentSubmerged Membrane Fact Sheet

Member Agency Treatment Facilities

In addition to the Water Authority, there are several other agencies that own and operate water treatment plants in the county.


California Fluoridation Regulations

Since the 1990s, state law has required water suppliers with 10,000 or more service connections or customers to fluoridate their water supply. The California Fluoridation Regulations adopted by the California Department of Health Services were added to the California Code of Regulations in April 1998.

Naturally occurring fluoride levels range from 0.1 to 0.4 parts per million, and water in San Diego County averages 0.23 parts per million. To reach the optimal range for dental health, fluoride must be added to reach 0.7 to 0.8 parts per million.

Agencies relying on the Water Authority for all of their treated water will receive fully optimized fluoride concentrations. Retail water agencies that blend Water Authority supplies with non-fluoridated supplies have lower fluoride levels. Systems that receive no treated water from the Water Authority have only naturally occurring levels of fluoride.

Flouridation Resources

San Diego County consumers can learn more about fluoride in their water by visiting the California State Department of Health or by contacting their local retail water provider.

MWD maintains a Water Quality Information Hotline at (800) 354-4420. Consumers with questions about whether they should adjust dental health practices should consult their dentist.

Lead Testing

Regular Lead Testing

The Water Authority regularly tests for the presence of lead and other potential contaminants in its supply sources and in the water it delivers to member agencies as part of its overall water quality monitoring program, using a range of techniques from real-time monitoring to laboratory testing.

Tests show no detectable levels of lead in any potable water from any treatment plant that serves the Water Authority.

The water source for the Carlsbad Desalination Plant is seawater from Agua Hedionda Lagoon, while the water source for the Skinner and Twin Oaks Valley treatment plants are from the State Water Project in Northern California and the Colorado River. Each of these sources is tested for lead annually in accordance with regulations from the U. S. Environmental Protection Agency and the State Water Resources Control Board, Division of Drinking Water. Local reservoirs are tested annually in accordance with state and federal water quality rules.

School Testing Regulations

Public concern over lead in other states’ drinking water supplies prompted the California Division of Drinking Water to enact a new requirement for the testing of water for lead in schools that took effect in 2018.

As of July 1, 2019, the Division of Drinking Water, in collaboration with the California Department of Education, has completed the initiative to test for lead in drinking water at all public K-12 schools.

Lead Resources

When lead is detected by customers, the most common cause is internal corrosion of plumbing systems and service lines that are the responsibility of the property owner. Consumers concerned about lead in drinking water can learn more on the EPA’s website or by calling the Safe Drinking Water Hotline at 1-800-426-4791. Bilingual service is available on the hotline.


Per- and polyfluoroalkyl substances (PFAS)

Per- and polyfluoroalkyl substances (PFAS) are a large group of synthetic chemicals that have been widely used in consumer, commercial and industrial products for their heat, water, and oil resistant properties. They are sometimes called “forever chemicals” because they break down very slowly in the environment. PFAS have been found in water, air, and soil around the world. PFAS can enter the sources of drinking water when products containing PFAS are used or spilled onto the ground or into lakes or rivers.

According to the U.S. Environmental Protection Agency (EPA), current scientific research suggests that exposure to certain PFAS may lead to adverse health outcomes. Certain PFAS, such as PFOS and PFOA, have been largely phased out due to health concerns. Research and studies are ongoing to learn more about different PFAS including:

  • Where PFAS is found in the environment
  • Ways to better detect and measure PFAS
  • How humans may be exposed to PFAS
  • Possible health effects from PFAS exposure
  • Treatment, management, and safe disposal

Drinking Water

The U.S. EPA and the California State Water Resources Control (State Water Board) are developing drinking water standards, or Maximum Contaminant Levels (MCLs), for PFAS at extremely low concentrations to protect consumers of drinking water. MCLs are enforceable standards that include a margin of safety. In California, the State Water Board has established health-based notification and response levels which require water systems to notify the public and implement management strategies if certain PFAS are detected at or above those levels.

Management options if PFAS are found in drinking water supplies include treatment, blending different supply sources to reduce concentrations, or removing individual groundwater wells from service until they are treated. Treatment to remove PFAS includes granular activated carbon (GAC) or reverse osmosis technologies.

The U.S. EPA began requiring PFAS monitoring in drinking water under its Uncontaminated Monitoring Rule (UCMR) in 2013. In California, the State Water Board increased requirements for PFAS monitoring in 2019. Testing for PFAS in drinking water supplies is increasing through expanded requirements and voluntary monitoring.

Regional Water Supplies

The Water Authority’s drinking supplies include imported water provided through the Metropolitan Water District and seawater desalination from the Carlsbad desalination facility. Metropolitan has infrequently found PFAS at very low levels just over the detection limits in some of its supply sources. The Water Authority’s seawater desalination supplies are treated with reverse osmosis which is known to remove PFAS.

More information about the Water Authority’s supply sources can be found on the facilities page. Water quality information is also provided by local water agencies in their annual consumer confidence reports. Find your local water agency’s website.