Updated
San Francisco's water travels from Yosemite, mostly untouched by filters
Most San Francisco tap water starts as Sierra Nevada snowmelt held in Hetch Hetchy Reservoir. It's some of the cleanest source water of any big U.S. city, and the clearest sign of that is that regulators don't require it to be filtered.
The supply, piece by piece
The city buys treated water from the San Francisco Regional Water System, a wholesale system that the SFPUC also owns and operates. It comes from several sources:
- Hetch Hetchy Reservoir: up to 85% of the water delivered each year. It's disinfected with UV light and chlorine, pH-adjusted, fluoridated and chloraminated, with no filtration.
- Alameda County reservoirs and upcountry non-Hetch Hetchy sources: filtered at the Sunol Valley Water Treatment Plant.
- San Mateo County reservoirs: filtered at the Harry Tracy Water Treatment Plant.
- Local groundwater: about 0.42% of San Francisco's 2025 supply, pumped from a deep aquifer in northern San Mateo County and the west side of the city and blended with surface water. The upcountry non-Hetch Hetchy sources weren't used in 2025. The regional system also took a small amount of treated water from a partner district, mainly in April and May.
The SFPUC says the mix of sources protects against drought, emergencies and disasters. It inspects the Hetch Hetchy watershed every year and the other watersheds every five years, and lists wildfire, wildlife, livestock and human activity as ongoing risks.
Soft, alkaline and chloraminated
| Parameter (2025) | Range | Average |
|---|---|---|
| Hardness (as CaCO3) | 8.1–112 ppm | 62 ppm |
| Sodium | 3.1–29 ppm | 18 ppm |
| pH | 9.0–9.7 | 9.3 |
| Alkalinity | 8–131 ppm | 64 ppm |
| Chloramine (as chlorine) | <0.1–3.6 ppm | 2.6 ppm (compliance value) |
An average of 62 ppm is about 3.6 grains per gallon, which is soft to slightly hard. Most San Francisco homes don't need a softener. The high pH is intentional corrosion control. Total trihalomethanes measured 12–65 ppb (compliance value 47, limit 80) and HAA5 measured 6–50 ppb (compliance value 37, limit 60).
Groundwater in the blend
The raw well water carries some chromium-6 (8.1–9.1 ppb) and nitrate (3.8–4.8 ppm as nitrogen), which the report attributes to natural deposits, landscape fertilizers and leaked wastewater. After blending, treated water in the system showed chromium-6 at only about 0.1 ppb. Because groundwater is such a small share of the supply, it barely changes what reaches the tap.
PFAS: none found
Under a 2025 California monitoring order, the SFPUC tested its active sources for 29 individual PFAS and detected none.
Lead: a city without known lead service lines
The SFPUC says its system has no known lead or galvanized service lines, and its plumbers have never seen a customer-owned lead line. The 2024 inventory confirmed no lead lines but still listed some lines as unknown material. Based on more than 500 site inspections and modeling, the utility estimates a 1% chance that any customer-side line contains lead, and it expects to resolve the unknowns by mid-2026, four years early. At 50 homes tested in 2024, the lead 90th percentile was 4.9 ppb (range under 1 to 8.8) and copper was 72 ppb. The next round of sampling is in 2027.
Lead in older San Francisco buildings usually comes from brass fixtures and solder. Flushing helps, and running the shower or a load of laundry counts. If you want a filter anyway, our filter selector matches certifications to what you want removed, and the filter vs. bottled cost calculator shows why bottled water rarely makes sense here.
San Francisco water FAQ
Why isn't Hetch Hetchy water filtered?
Hetch Hetchy Reservoir water is exempt from state and federal filtration requirements because of its exceptional quality. The SFPUC disinfects it with ultraviolet light and chlorine, adjusts the pH for corrosion control, adds fluoride and then converts the disinfectant to chloramine. Water from the Bay Area reservoirs is filtered at the Sunol Valley and Harry Tracy plants.
Can I use San Francisco tap water in my aquarium?
Not straight from the tap. San Francisco uses chloramine, which doesn't evaporate when water sits out the way chlorine does, and it's harmful to fish. Use a conditioner that neutralizes chloramine. People on kidney dialysis also need water treated to remove it.
How do I get my water tested for lead in San Francisco?
Call 311 or visit sfpuc.gov/LeadTest. The SFPUC tests for lead for $25 per tap. Clients of the Women, Infants and Children (WIC) program run by the San Francisco Department of Public Health can get free test vouchers.
Why does hardness vary so much in San Francisco?
The 2025 range was 8.1 to 112 ppm. Hetch Hetchy snowmelt is very soft. Water from local reservoirs and the small amount of blended groundwater carries more minerals, so readings rise when more of that water is in the mix.
Sources
- SFPUC, City of San Francisco 2025 Annual Water Quality Report
- SFPUC lead testing
- California State Water Resources Control Board PFAS program
Reviewed November 1, 2026 against the sources above. Public water system ID CA3810011 (San Francisco Public Utilities Commission). Figures describe the utility's system, not your home's plumbing; a certified lab test tells you what comes out of your tap. Spot an error? Tell us.