Window Washing in San Francisco

SFPUC reports hardness as a range rather than a point: 8.1 to 112 ppm in the 2025 report, averaging 62. The bottom of that span is Hetch Hetchy water, Sierra snowmelt off granite with almost nothing dissolved in it; the top is local Alameda and Peninsula watershed supply, which is materially harder. Which one dominates depends on the season and on how dry the year has been.

The blend is not theoretical. A large institutional customer on the SFPUC system publishes its own incoming readings and has recorded 22 mg/L on a Hetch Hetchy-dominated blend and 129 on a blend leaning on the Sunol Valley plant — a six-fold swing in the same pipes within weeks. A crew that sets its rinse policy in a wet year will find it wrong in a dry one.

Finished pH averages 9.3 and ranges to 9.7, among the most alkaline on this site and higher than Fargo. That is the single most useful fact about San Francisco water for this trade: an alkaline cleaner arrives with nothing pulling against it, so dilute well below the label rate and rinse sooner than instinct says. Strong mixes streak here rather than clean harder.

Very soft water is aggressive water, and the city's building stock is old enough for that to matter. SFPUC doses to manage it, but the combination of low-mineral supply and Victorian-era plumbing is why lead-certified filtration is a live local recommendation — worth knowing because it shapes what customers already believe about their water before a crew arrives.

Marine fog is the real operating challenge and it is not a mineral problem. Afternoon and overnight fog condenses on west-facing glass and redeposits marine salts, so a pane finished clean at noon can be spotted by the following morning. The film is hygroscopic: it softens and spreads in damp air rather than drying hard.

The fog gradient across the city is steep enough to price by. The outer Sunset and Richmond sit in it most of the year; the Mission and Potrero are often in sun on the same afternoon. Two houses four miles apart on identical water need genuinely different service intervals.

Victorian and Edwardian original glazing in Pacific Heights, Alamo Square and the Western Addition does not take a scraper. Soft putty, wavy glass and ornate divided lights mean softer pressure and pure-water systems, and the loss from a confident blade is permanent.

The Financial District's high-rise elevations are rope-access and suspended-platform work under California's own regulatory regime, a separate trade from the residential book rather than an extension of it — and the ceiling on revenue in this market.

The Pacific coast from San Diego to Eureka sees salt aerosol year-round, heaviest during winter storm season. The Marin headlands, the San Francisco Sunset, the Big Sur coast, and the Malibu beach properties are the heaviest-deposition areas. Salt corrodes aluminum sash hardware over time.

The Bay Area summer fog produces sustained morning condensation on east-facing exposures that redeposits atmospheric particulate as a thin film. Standard cleaning protocols work; the consideration is the cleaning cadence — coastal SF and the Marin shoreline want more frequent service than inland equivalents.