If a water report gives a mineral range, the range is part of the answer. Replacing it with one tidy number makes the report easier to repeat but less useful. San Francisco’s annual report gives readers enough detail to avoid that shortcut: a reporting period, units, an average and an explanation of source variation.
Hardness generally concerns dissolved calcium and magnesium, as the US Geological Survey explains. For the local values, use SFPUC’s report rather than applying a general hardness definition as if it were a sample from your tap.
Read the range, average and unit together
SFPUC’s 2025 Annual Water Quality Report includes general mineral information alongside its other tables. The 2025 hardness row is reported as calcium carbonate, CaCO3, in parts per million, or ppm. The range is 8.1 to 112 ppm and the average is 62 ppm.
Those values belong to the report’s sampling period. The average is a summary of the reported results, not a promise that an accommodation’s water has that exact hardness today. Nor does the upper end tell you that every tap reached that value.
Keep the substance, unit and year in your notes when comparing reports. A number copied without its row label can look comparable even when it describes something else. The hardness convention matters too: “as CaCO3” is part of how this particular result is expressed, not a label to discard for a shorter headline.
Blending changes the context of a value
The report explains that source blending through the year caused varying water quality. Read the range as variation across that reporting period, without assigning one permanent setting to the whole city.
SFPUC’s groundwater program page says local groundwater is treated and blended with surface water before delivery to customers. The page also points readers towards blend information. We did not retrieve its linked map or report for a property, so no blend proportion is assigned to an address here.
For a practical question about an appliance, ask for the current local hardness information relevant to the supply. The annual row is a starting point for understanding variation, rather than an instruction to enter its average into every dishwasher.
Check which water the table describes
The report also has separate tables for local groundwater before and after treatment. A value from a raw-water column should not be relabelled as the water supplied at a household tap. The table heading and footnotes keep those different records apart.
SFPUC’s report-reading guidance explains ppm, ppb and ppt as different concentration scales. Preserve the stated unit when comparing any rows. The report’s year is equally important, and footnotes in other tables may identify a different testing period.
A tap problem needs its own question
A mineral range cannot diagnose unexpected particles or colour at a building. SFPUC’s discolored-water guidance lists rust or sediment in distribution or home piping among possible causes. Its discussion of white particles includes mineral deposits and material from a water-heater dip tube. These are possibilities, not a diagnosis made from a photograph or this article.
For a water-quality concern, that page gives 3-1-1 from within San Francisco or 415-701-2311 from outside. Tell the utility or your host what you observed rather than concluding “just minerals” from the annual table.
Our San Francisco guide adds travel context. For equipment questions, the pitcher-filter and softener guide helps separate the jobs people often bundle together.
