San Francisco’s tap water is generally considered safe to drink and is often ranked among the best in the nation. The quality is managed by the San Francisco Public Utilities Commission (SFPUC), which oversees a vast system serving the city and wholesale customers in three surrounding Bay Area counties. The water consistently meets all federal and state regulatory standards for health and safety.
The Pristine Source of San Francisco’s Water Supply
The majority of San Francisco’s water originates from the high Sierra Nevada mountains, specifically the Hetch Hetchy Reservoir within Yosemite National Park. This watershed is exceptionally protected, situated on federally managed land, and receives its water primarily from snowmelt. The raw water quality is so high that the SFPUC has been granted a Filtration Avoidance Waiver by the U.S. Environmental Protection Agency (EPA) and the State Water Resources Control Board.
This high-quality source water travels nearly 160 miles to the Bay Area, mainly through a gravity-fed system that requires minimal pumping. The system also utilizes local reservoirs on the Peninsula and in the East Bay, such as the Crystal Springs and San Antonio reservoirs, to supplement the Hetch Hetchy supply. Water drawn from these local sources, however, requires a more comprehensive treatment process due to their proximity to urban and agricultural areas.
The Multi-Stage Water Treatment and Purification Process
The treatment for the main Hetch Hetchy supply is unique because it is not filtered. Instead, this water is treated with modern disinfection techniques at the Tesla Treatment Facility. The process includes disinfection using ultraviolet (UV) light followed by chlorine to neutralize potential pathogens.
Additionally, the SFPUC adjusts the water’s pH by adding lime to minimize corrosiveness and prevent the leaching of metals from pipes. Fluoride is also added to the water as a public health measure to promote dental health. Water from the supplementary local reservoirs must undergo full conventional treatment, including coagulation, flocculation, sedimentation, and filtration, before being disinfected.
A secondary disinfectant, chloramine, which is a combination of chlorine and ammonia, is then added to the water before it enters the distribution system. Chloramine is more stable than chlorine alone and maintains a consistent disinfectant residual throughout the extensive pipe network. This chemical choice also helps to reduce the formation of regulated disinfection byproducts, such as trihalomethanes, which can form when chlorine reacts with organic matter in the water.
Regulatory Compliance and Current Safety Assessment
The San Francisco Public Utilities Commission rigorously tests the water to ensure it meets the strict standards set by the EPA and the State Water Resources Control Board’s Division of Drinking Water. The SFPUC conducts tens of thousands of tests annually, monitoring for microbiological contaminants, inorganic compounds, organic chemicals, and disinfection byproducts. The most recent water quality reports confirm full compliance with all federal and state Maximum Contaminant Levels (MCLs).
PFAS and Disinfection Byproducts
The SFPUC has proactively tested for per- and polyfluoroalkyl substances (PFAS), also known as “forever chemicals,” and has not detected any of these compounds in the drinking water supply. This proactive testing goes beyond current regulatory requirements for many utilities and helps address common consumer concerns.
While the SFPUC ensures the water is safe as it leaves the treatment plants, trace amounts of disinfection byproducts, such as trihalomethanes and haloacetic acids, are occasionally found. These compounds are a natural result of the disinfection process but remain well within the legal limits established by regulatory bodies. The high frequency of testing, which includes samples taken from various points in the distribution system, confirms that the water quality is consistently maintained before it reaches customer property lines.
Understanding Local Infrastructure and Delivery Risks
Even with a high-quality source and comprehensive treatment, the water’s final quality is influenced by the pipes it travels through to reach the tap. The SFPUC removed all known utility-owned lead service lines—the pipe connecting the water main to the property line—in the 1980s. This action significantly reduced the primary risk of widespread lead contamination from the city’s infrastructure.
However, potential contamination risks still exist within the customer-owned plumbing inside private residences and older commercial buildings. This includes lead from brass fixtures, older faucets, and lead solder used in plumbing installed before 1986. The SFPUC’s corrosion control process, which adjusts the water’s pH, helps to form a protective coating inside pipes to minimize the leaching of these metals.
Older galvanized pipes, even if not originally lead, can also pose a risk if they have trapped lead particles from previously connected lead service lines. For residents concerned about the plumbing in their specific building, a simple step is to flush the tap for 30 seconds to several minutes, especially after the water has been sitting unused for several hours. This action ensures any water that may have absorbed metals from internal plumbing is cleared before it is consumed.