San Francisco’s water information uses both “filtered” and “unfiltered” because treatment depends on the source route. An exemption from filtration is not an exemption from treatment. SFPUC describes disinfection for Hetch Hetchy water and filtration for water passing through its local reservoir treatment routes.
For a reader, the first question is which source the statement concerns. Then follow the named treatment stages. A single word such as “unfiltered” leaves out much of the process and does not describe every route in the regional system.
Filtration removes particles
SFPUC’s treatment-process explanation describes filters made from anthracite coal and sand to remove small suspended particles. Its description separates that stage from disinfection, which concerns killing or inactivating pathogens.
Where a plant uses both, filtration removes material and disinfection controls pathogens through the stated process. Neither word alone establishes every substance in the water or certifies a household product.
A filter-media model shows a concept without establishing actual filter depth, operating conditions or a removal percentage. Use relevant plant or product evidence for those details.
An unfiltered source is still disinfected
The 2025 Annual Water Quality Report says Hetch Hetchy water is exempt from filtration requirements. It then describes ultraviolet light and chlorine disinfection, pH adjustment, fluoridation and chloramination.
The process page names Tesla Treatment Facility for UV and chlorine disinfection. That makes “unfiltered” a description of a particular treatment route, not a synonym for untreated reservoir water. It gives no reason to apply the exemption to water collected directly from a lake.
The EPA’s rule summary ties filtration avoidance to source quality and watershed-protection criteria. That is a specific framework, not a blanket exemption based on a city name. We did not retrieve the individual waiver instrument for this article.
Local reservoir water follows filtration routes
The utility identifies Sunol Valley and Harry Tracy water treatment plants as using filtration. The annual report describes these routes separately from the Hetch Hetchy treatment account. Keep that source distinction when summarising what San Francisco’s water receives.
The report concerns 2025. It does not assign one fixed proportion of those routes to an accommodation today. The process page is undated, and its project-stage wording does not establish that construction is complete or a new process is operating.
Treatment continues into the distribution story
The CDC explains that UV treatment does not continue disinfecting water as it moves through distribution pipes. SFPUC separately describes chloramine maintained in the distribution system. Those descriptions help explain why a treatment account can mention both a UV stage and a continuing disinfectant residual.
Follow the whole stated treatment route when comparing water sources. If you are considering a household device, check the exact claim it is meant to address; our filter-certification guide explains how to read those claims. A municipal process description is not evidence that an unrelated device achieves the same result.
Our San Francisco guide gives travel context. For a particular property or an active instruction, use the relevant local information. No current household sample or individual tap result was obtained here.
