Water Quality
The San Francisco Regional Water System (SFRWS) regularly collects and tests water samples from reservoirs and designated sampling locations throughout the system to ensure that the water delivered to you meets all federal and state drinking water standards. In 2024, the SFRWS conducted more than 45,650 drinking water tests of samples from source and transmission system locations. This is in addition to the extensive treatment process control monitoring performed by our certified operators and online instruments.
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 (USEPA) and the State Water Resources Control Board (SWRCB) 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.
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MPWD 2024 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
Our drinking water supply consists of surface water and groundwater that are well protected and carefully managed. The surface water is stored in reservoirs in the Sierra Nevada, Alameda County, and San Mateo County, and the groundwater is kept in a deep aquifer in the northern part of San Mateo County. Maintaining this variety of sources is an important component of the near- and long-term water supply management strategy of the San Francisco Regional Water System (SFRWS). 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.
To meet drinking water standards for human consumption, all surface water the SFRWS supplies must undergo proper treatment. Water from Hetch Hetchy Reservoir is exempt from state and federal filtration requirements due to its exceptional quality. It undergoes 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 are delivered to the Sunol Valley Water Treatment Plant. Water from reservoirs in San Mateo County is delivered to the Harry Tracy Water Treatment Plant. Water treatment at these plants consists of filtration, disinfection, fluoridation, taste and odor removal, and optimum corrosion control. In 2024, neither upcountry non-Hetch Hetchy sources of water nor groundwater was used.
Protecting Our Watersheds
The SFRWS conducts watershed sanitary surveys for the Hetch Hetchy source annually and for non-Hetch Hetchy surface water sources every five years. The latest sanitary surveys for the non-Hetch Hetchy watersheds were completed in 2021 for the period of 2016-2020. These surveys document the SFPUC’s stringent watershed protection activities that are implemented with support from partner agencies including the National Park Service and the United States Forest Service.
These surveys not only evaluate the sanitary conditions and water quality of the watersheds but also describe 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 SWRCB Division of Drinking Water at 510-620-3474 for more information.
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 Immunodeficiency Syndrome or other immune system disorders, some elderly, 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 surface water. We regularly test for this waterborne pathogen and found it at very low levels in source water and treated water in 2024. However, current test methods approved by the United States Environmental Protection Agency (USEPA) do not distinguish between dead organisms and those capable of causing disease. Ingestion of Cryptosporidium may cause cryptosporidiosis with 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.
Guidelines on appropriate means to lessen the risk of infection by Cryptosporidium and other microbial contaminants are available from the USEPA’s Safe Drinking Water Hotline at (800) 426-4791 or at epa.gov/safewater
Boron Detection Above Notification Level in Source Water
In 2024, boron was detected at a level of 2.3 parts per million (ppm) in the raw water stored in Pond F3 East, one of the SFRWS’s approved sources in the Alameda Watershed. Similar levels were detected in the same pond in preceding years. Although the detected value was above the California Notification Level of 1 ppm, the water was typically delivered to San Antonio Reservoir where it was substantially diluted to below the Notification Level before treatment at the Sunol Valley Water Treatment Plant and delivery to customers. Boron is an element in nature and is typically released into air and water when soils and rocks naturally weather.
Lead and Drinking Water
Exposure to lead, if present, can cause serious health effects in people of all ages, especially for pregnant women and young children. Infants and children who drink water containing lead could have decreases in intelligent quotient and attention span as well as increases in learning and behavior problems. The children of women who are exposed to lead before or during pregnancy can have an increased risk of these adverse health effects. Adults can have increased risks of heart disease, high blood pressure, kidney, or nervous system problems.
Lead in drinking water is primarily from materials and components associated with service lines and home plumbing. 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. Because lead levels may vary over time, lead exposure is possible even when your tap sample results do not detect lead at one point in time. You share the responsibility for protecting yourself and your family from the lead in your home plumbing by taking one or more of the following actions:
- Identify and remove lead materials within your home plumbing.
- If you use a water filter, make sure it’s certified for lead to National Sanitation Foundation (NSF)/ANSI standards. Make sure to replace and maintain the filter according to the manufacturer’s instructions.
- Use only cold water for drinking, cooking, and making baby formula. (Do not boil your water to remove lead. Boiling water will not remove lead).
- Flush your pipes for several minutes before using your water for drinking, cooking, and preparing baby formula (this can be done by running your tap, taking a shower, doing laundry or a load of dishes, or reusing for watering plants).
- Flush for a longer period if you have pipes made of lead or galvanized material. Visit sfpuc.gov/lead to see an instructional video if you would like to test your pipes.
If you are concerned about lead in your water, you can have your water tested. Information about lead in drinking water, testing methods, and steps you can take to minimize exposure is available at epa.gov/safewater/lead
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. Based on the recommendation from the Centers for Disease Control and Prevention (CDC) and the State Water Resources Control Board’s (SWRCB) regulatory guidance, the San Francisco Public Utilities Commission has maintained an optimal fluoride level at 0.7 milligram per liter (mg/L, or part per million, ppm), since 2015. The optimal level provides the benefits of tooth decay prevention while minimizing the chance that children develop dental fluorosis. Infants fed formula mixed with water containing fluoride at this level may still have a chance of developing mild to very mild fluorosis, which can cause tiny white lines or streaks in their teeth. These marks are often only visible under a microscope. Even in cases where the marks are visible, they do not pose any health risk. To lessen the 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, toothpaste, 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.
No PFAS Detected
PFAS are man-made chemicals that have been used in industrial and consumer products since the 1940s. We did not detect PFAS in our water. To learn more, CLICK HERE.
Unregulated Contaminant Monitoring Rule
The SFRWS conducted four consecutive quarters of monitoring at designated locations approved by the United States Environmental Protection Agency in 2024, and all results have been non-detected.
Lead and Copper Tap Sampling Results
The Mid-Peninsula Water District conducted its triennial residential Lead and Copper Rule (LCR) monitoring in August 2024. This sampling is conducted by residents inside their home at their faucet tap. The tap sampling results for copper and lead were below regulatory requirements based on the 90th percentile. If any MPWD customers are interested in participating in the next round of the triennial LCR monitoring in 2027, please contact the District office at (650) 591-8941.
Taste, Odor, or Discolored Water Issue?
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.