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IMPORTANT CHLORAMINE NOTICE: The District gets its water from the San Francisco Water Department (SFPUC). The SFPUC uses chloramine (a mixture of chlorine and ammonia) to disinfect the water. Chloraminated water is safe for people and animals; however, precautions must be taken to remove or neutralize chloramine during kidney dialysis process, in the preparation of water for fish tanks and ponds, and for businesses requiring highly processed water. Please ask District personnel for additional information.

image of family drinking clean water

The Westborough Water District provides its customers with high quality drinking water that is safe to drink and meets standards set by the California Department of Health Services and the United States Environmental Protection Agency.

The Westborough Water District receives 100 percent of its water from the San Francisco Water Department. The water comes from Hetch Hetchy in Yosemite National Park and local reservoirs.

The California Department of Health Services and the United States Environmental Protection Agency set standards for drinking water quality.

The District collects samples throughout the system weekly to be analyzed for coliform bacteria, chlorine residual, pH, and turbidity. Every three months the District collect samples to monitor for trihalomethanes, or THMs, compounds formed when the chlorine used for disinfection reacts with naturally occurring organic compounds found in water. Water quality is monitored daily at the Harry Tracy treatment plant by the San Francisco Water Department.

Water Quality Reports

Our Drinking Water Sources and Treatment

The San Francisco Regional Water System’s (SFRWS) 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. The groundwater source is a deep aquifer in northern San Mateo County. Maintaining these sources is an important component of our near- and long-term water supply management. A diversity of sources not only protects us from potential disruptions due to emergencies or natural disasters but also provides resiliency during periods of drought. It helps us ensure a sustainable water supply as we address issues such as climate uncertainty, regulatory changes, and population growth.

The Westborough Water District purchases 100% of its water from the San Francisco Public Utility Commission (SFPUC). All surface water we deliver to you undergo proper treatment approved by the regulatory agencies. Water from Hetch Hetchy Reservoir is exempt from state and federal filtration requirements due to its exceptional quality. However, it is still subject to 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. Raw water from local reservoirs in Alameda County and upcountry non-Hetch Hetchy sources are delivered to the Sunol Valley Water Treatment Plant. Similarly, 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 2025, neither the SFRWS’s upcountry non-Hetch Hetchy sources nor its groundwater wells were used; however, the SFRWS imported a very small amount (0.38%) of treated water from Valley Water District in April and May.

Water Quality

Clean glass of drinking water sitting on a rock

The SFRWS regularly tests water from reservoirs and designated sampling locations throughout the system. In 2025, the SFRWS performed more than 45,550 drinking water tests. This is in addition to the extensive treatment process monitoring conducted by the 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. Collectivel 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.

Tuolumne Watershed in the SierrasProtection of Watersheds

The SFRWS conducts watershed sanitary surveys for its Hetch Hetchy source annually and for the non-Hetch Hetchy surface water sources every five years. The latest sanitary surveys for the non-Hetch Hetchy watersheds were completed in 2021. These surveys summarize the following:

  • Sanitary conditions of the watersheds
  • Water quality of the reservoirs in the watersheds
  • The SFRWS’s stringent watershed protection activities that are implemented with support from its partner agencies including the National Park Service and the United States Forest Service
  • Results of watershed management activities conducted in prior years
Overall, 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.

image of two children drinking water from a glassSpecial 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.

The SFRWS regularly tests for Cryptosporidium, a waterborne parasitic microbe that may be spread through means other than drinking water. As in the past, this pathogen was found at very low levels in source water and treated water in 2025. Current test methods approved by the United States Environmental Protection Agency (USEPA) do not distinguish between dead organisms and those capable of causing disease. Cryptosporidium must be ingested to cause cryptosporidiosis with symptoms of nausea, abdominal cramps, diarrhea, and associated headaches.

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 www.epa.gov/safewater

Sunol Valley Water Treatment PlantImportant Notice About Water Monitoring

The SFPUC is required to notify its customers of a monitoring violation within one year after it learns of the violation. This notice is to inform you that the SFRWS, which is operated by the SFPUC, failed to monitor for recycled filter backwash water turbidity (very small or microscopic particles in the water) at its Sunol Valley Water Treatment Plant (SVWTP) from June 23, 2025, to July 2, 2025. This monitoring violation was the result of equipment failure and was corrected on July 3, 2025, as soon as it became apparent to plant staff. Even though this failure was not an emergency and did not impact water quality, as our customers, we want you to know what happened and what we did to correct this situation.

Treated or “backwash” water is used to wash the filters at the treatment plant after they have completed a run cycle. Instead of wasting this backwash water, the SVWTP treats it and then recycles it to the front of the plant where it blends with the source or lake water and then goes through the whole treatment process again. Monitoring at downstream locations at the SVWTP indicated that the plant’s effluent or final product was consistently of very high quality and exceeded all drinking water standards.

There is nothing you need to do at this time. The instrument (turbidimeter) that monitors turbidity for the recycled water was not operating during the period mentioned above. The instrument was subsequently repaired and put back into operation on July 3, 2025, and since that time the daily monitoring of recycled filter backwash water turbidity has resumed with no interruption. Operations staff was retrained on monitoring requirements and additional operational and maintenance activities were implemented to prevent a recurrence. If you need more information, please contact the resources listed on the last page of this report.

This notice is provided by the Westborough Water District, CA4110027 on behalf of the SFRWS and distributed by June 30, 2026

No Poly-fluoroalkyl Substances (PFAS) Detected

You may have heard about PFAS. These are man-made chemicals that have been used in industry and consumer products worldwide since the 1940s. We did not detect PFAS in our water. To learn more, visit waterboards.ca.gov/pfas

Fluoridation

We add fluoride to our water. California law mandates fluoridation. It is proven safe. It is also effective at preventing and controlling tooth decay. Our fluoride levels match the state’s optimal level. To learn more, CLICK HERE or go to the CDC website cdc.gov/fluoridation

Drinking Water and Lead

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 (American National Standards Institute). 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 www.epa.gov/safewater/lead.

Lead Service Line Inventory & Replacement

As previously reported, we completed an inventory of lead user service lines (LUSL) in our system and there are no known pipelines and connectors between water mains and meters made of lead. Our policy is to remove and replace any LUSL promptly if it is discovered during pipeline repair and/or maintenance.

In 2024, the Westborough Water District conducted an Initial Lead Service Line Inventory (LSLI) and there were no water system owned or customer owned lead service lines.

Lead and Copper Tap Sampling Results

We conducted the triennial Lead and Copper Rule (LCR) monitoring in 2025, and none of the 30 samples collected at the consumer taps had lead or copper concentrations above the action levels. The next round of LCR monitoring will be conducted in 2028.

Boron Detection Above Notification Level in Source Water

In 2025, Boron was detected at levels of 1.8 and 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 of boron were detected in the same pond in preceding years. Although the detected values were higher than the California Notification Level (NL) of 1 ppm, the water was normally delivered to, or blended in the influent pipeline with water from, San Antonio Reservoir. Blending in either way has substantially diluted boron level well below 1 ppm NL prior to 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 naturally weather.

Urban Water Management Report

In compliance with the Urban Water Management Planning Act, the Westborough Water District (WWD.) has prepared its sixth updated Urban Water Management Plan (UWMP) under the terms of AB797 (1983) and subsequent amending legislation.

On June 11, 2026, this plan will be presented at a Public Hearing to be approved by the WWD Board of Directors. It supercedes the existing plan prepared in 2020, and will be used by the District staff to guide the District's water conservation efforts through the year 2030.

Click here for 2025 Urban Water Management Report (UWMP) (PDF)

Click here for 2020 Urban Water Management Report (UWMP) (PDF)

Click here for 2015 Urban Water Management Report (UWMP) (PDF)