Water Quality

image of water quality icon

As water travels over the surface of the land or through the ground, it dissolves naturally occurring minerals and, in some cases, radioactive material, and can pick up substances resulting from the presence of animals or human activity. Collectively, these are called contaminants. Therefore, drinking water, including bottled water, may reasonably be expected to contain at least small amounts of some contaminants. The presence of contaminants does not necessarily indicate that water poses a health risk. To ensure that tap water is safe to drink, the United States Environmental Protection Agency and the State Water Resources Control Board prescribe regulations that limit the amount of certain contaminants in water provided by public water systems. The United States Food and Drug Administration regulations and California law also establish limits for contaminants in bottled water that provide the same protection for public health.

The San Francisco Regional Water System (SFRWS) regularly collects and tests water samples from reservoirs and designated sampling locations throughout its system to ensure the water delivered to you meets all state and federal drinking water standards. In 2023, the SFRWS conducted more than 49,610 drinking water tests in the source, transmission, and distribution system. This is in addition to its extensive treatment process control monitoring performed by certified operators.

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Cover of MPWD's 2023 Consumer Confidence Report.

MPWD 2023 Consumer Confidence Report
(Annual Water Quality Report)

Water quality results are published annually in the MPWD Consumer Confidence Reports (CCRs).

Drinking Water Sources and Treatment

The SFRWS’s drinking water supply consists of surface water and groundwater that are well protected and carefully managed. These sources are diverse in both origin and location with the surface water stored in reservoirs located in the Sierra Nevada, Alameda County and San Mateo County, as well as groundwater stored in a deep aquifer located in the northern part of San Mateo County. Maintaining this variety of sources is an important component of our near- and long-term water supply management strategy. A diverse mix of sources protects us from potential disruptions due to emergencies or natural disasters, provides resiliency during periods of drought, and helps us ensure a long-term, sustainable water supply as we address issues such as climate uncertainty, regulatory changes, and population growth.

SFPUC Water System Map

To meet drinking water standards for consumption, all surface water sources, including the upcountry non-Hetch Hetchy sources, undergo treatment before it is delivered to our customers. While the water from Hetch Hetchy Reservoir is exempt from state and federal filtration requirements, it does receive the following treatment before being delivered for your consumption: disinfection using ultraviolet light and chlorine, pH adjustment for optimum corrosion control, fluoridation for dental health protection, and chloramination for maintaining disinfectant residual and minimizing the formation of regulated disinfection byproducts. Water from local Bay Area reservoirs in Alameda County and upcountry non-Hetch Hetchy sources is delivered to Sunol Valley Water Treatment Plant; whereas water from local reservoirs in San Mateo County is delivered to Harry Tracy Water Treatment Plant. Water treatment at these plants consists of filtration, disinfection, fluoridation, optimum corrosion control, and taste and odor removal. In 2023, neither upcountry non-Hetch Hetchy sources nor groundwater was used by the SFRWS.

Protecting Our Watersheds

Image of the Tuolumne River

The San Francisco Regional Water System (SFRWS) conducts watershed sanitary surveys for its Hetch Hetchy source annually and every five years for its local water sources and upcountry non-Hetch Hetchy sources. The latest sanitary surveys for the non-Hetch Hetchy watershed were completed in 2021 for the period of 2016-2020. All these surveys together with our stringent watershed protection management activities were completed with support from partner agencies including the National Park Service and the United States Forest Service. The purposes of these annual and quinquennial surveys are to evaluate the sanitary conditions and water quality of the watersheds and to review the results of watershed management activities conducted in the preceding years. Wildfire, wildlife, livestock, and human activities continue to be the potential contamination sources. You may contact the San Francisco District office of the State Water Resources Control Board’s Division of Drinking Water at 510-620-3474 for more information.

image of two children drinking water from glasses.

Special Health Needs

Some people may be more vulnerable to contaminants in drinking water than the general population. Immunocompromised persons, such as those with cancer undergoing chemotherapy, persons who have undergone organ transplants, people with Human Immunodeficiency Virus/Acquired Immuno-deficiency Syndrome or other immune system disorders, and some elderly people and infants, can be particularly at risk from infections. These people should seek advice about drinking water from their healthcare providers.

Cryptosporidium is a parasitic microbe found in most surface water. The SFRWS regularly tests for this waterborne pathogen and found it at very low levels in source water and treated water in 2023. However, current test methods approved by the United States Environmental Protection Agency do not distinguish between dead organisms and those capable of causing disease. Ingestion of Cryptosporidium may produce symptoms of nausea, abdominal cramps, diarrhea, and associated headaches. Cryptosporidium must be ingested to cause disease, and it may be spread through means other than drinking water.

The United States Environmental Protection Agency (EPA) and the Centers for Disease Control and Prevention guidelines on appropriate means to lessen the risk of infection by Cryptosporidium and other microbial contaminants are available from the EPA’s Safe Drinking Water Hotline at 800-426-4791 or at epa.gov/safewater

Boron Detection Above Notification Level in Source Water

In 2023, boron was detected at a level of 1.7 ppm (parts per million) in the raw water stored in Pond F3 East, one of the SFRWS’s approved sources in the Alameda Watershed. Similar levels were also previously detected in the same pond. Although the detected value was above the California Notification Level (NL) of 1 ppm, the water was typically delivered to San Antonio Reservoir, where it was substantially diluted to below the NL before treatment at the Sunol Valley Water Treatment Plant. Boron is an element in nature and is typically released into air and water when soils and rocks weather naturally. 

Lead and Drinking Water

Exposure to lead, if present, can cause serious health effects in all age groups, especially for pregnant women and young children. Infants and children who drink water containing lead could have decreases in IQ and attention span and increases in learning and behavior problems. The children of women who are exposed to lead before or during pregnancy can have increased risk of these adverse health effects. Adults can have increased risks of heart disease, high blood pressure, kidney, or nervous system problems.

When lead is found to be present in drinking water, it is primarily from materials and components associated with service lines and home plumbing. There are no known lead service lines in our water distribution system. We are responsible for providing high quality drinking water and removing lead pipes, but we cannot control the variety of materials used in plumbing components in your home. You share the responsibility for protecting yourself and your family from lead in your home plumbing. You can take responsibility by identifying and removing lead materials within your home plumbing and taking steps to reduce your family’s risk. Before drinking tap water, flush your pipes for several minutes by running your tap, taking a shower, doing laundry or a load of dishes. You can also use a filter certified by an American National Standards Institute accredited certifier to remove lead from drinking water. If you are concerned about lead in your water and wish to have your water tested, call Mid-Peninsula Water District at (650) 591-8941 to request a lead test. Information about lead in drinking water, testing methods, and steps you can take to minimize exposure is available at USEPA website www.epa.gov/safewater/lead

Mid-Peninsula Water District is currently conducting a lead service line (LSL) inventory to identify the materials of service lines connected to the public water distribution system. This inventory will include the service line material from the water main to the water meter, as well as the pipe material behind the water meter to the inlet of the home or building. The LSL inventory is anticipated to be completed by October 16, 2024.

Fluoridation and Dental Fluorosis

Mandated by State law, water fluoridation is a widely accepted practice proven safe and effective for preventing and controlling tooth decay. Our fluoride target level in the water is 0.7 milligram per liter (mg/L, or part per million, ppm), consistent with the May 2015 State regulatory guidance on optimal fluoride level. Infants fed formula mixed with water containing fluoride at this level may still have a chance of developing tiny white lines or streaks in their teeth. These marks are referred to as mild to very mild fluorosis, and are often only visible under a microscope. Even in cases where the marks are visible, they do not pose any health risk. The Centers of Disease Control (CDC) considers it safe to use optimally fluoridated water for preparing infant formula. To lessen this chance of dental fluorosis, you may choose to use low-fluoride bottled water to prepare infant formula. Nevertheless, children may still develop dental fluorosis due to fluoride intake from other sources such as food, tooth paste, and dental products. Contact your healthcare provider or the SWRCB if you have concerns about dental fluorosis. For additional information about fluoridation or oral health, visit the SWRCB website here or the CDC website www.cdc.gov/fluoridation

No PFAS Detected

PFAs are man-made chemicals that have been used in the industry and comsumer products since the 1940s. We did not detect PFAS in our water. To learn more, CLICK HERE.

Unregulated Contaminant Monitoring Rule

The fifth Unregulated Contaminant Monitoring Rule (UCMR 5) was published on December 27, 2021. UCMR 5 requires sample collection for 30 chemical contaminants between 2023 and 2025 using analytical methods developed by the EPA and consensus organizations. UCMR 5 will provide new data that will improve the agency’s understanding of the frequency that 29 per- and polyfluoroalkyl substances (PFAS) and lithium are found in the nation’s drinking water systems, and at what levels. The monitoring data on PFAS and lithium will help the EPA make determinations about future regulations and other actions to protect public health under the Safe Drinking Water Act (SDWA). In 2023, the MPWD conducted 4 quarter sampling of the 29 polyfluoroalky substances and lithium. The results for the samples taken in the 4 quarters were non-detect (ND).

Lead and Copper Tap Sampling Results

The Mid-Peninsula Water District conducted its triennial residential Lead and Copper Rule (LCR) monitoring in August 2021, and all the tap sampling results were all below the lead and copper action level. The Mid-Peninsula Water District is currently conducting its triennial LCR monitoring District-wide with a scheduled completion date of October 2024. The results will be published next year in the MPWD’s 2024 Consumer Confidence Report.

Taste, Odor, or Discolored Water Issue?

water quality image of water glass being filled by kitchen faucet

Opening a faucet or two in your home or business, or an outside spigot, to let the water run for a couple of minutes should resolve it. Remember to capture the water in a bucket to use for watering indoor plants or outdoor landscaping!

Depending upon the water turnover in the mainline serving your connection, or seasonal fluctuations in water treatment by San Francisco Water, a temporary water quality issue could be quickly resolved with a mini-flushing of your service line.

You can now use MPWD's online Water Quality Self Diagnosis Tool to help determine possible causes and solutions of typical water quality issues experienced in a home. If the problem persists, please contact us at 650-591-8941 or online here.