Window Washing in New York City

DEP publishes hardness as about 1.8 grains per gallon citywide, roughly 31 mg/L, and then immediately qualifies it: water from the Croton watershed is moderately hard, water from the Catskill/Delaware watershed is soft or slightly hard, and New Yorkers receive one, the other, or a blend of both. This is an operator telling customers plainly that a single citywide number does not describe their tap.

In the blend areas DEP states hardness can reach 7 grains per gallon — around 120 mg/L, which the department itself calls moderately hard. That is roughly four times the citywide average inside one municipal system. A crew working a Croton-blend neighbourhood and a crew working pure Catskill/Delaware are handling materially different water while quoting the same city.

Because the range moves by watershed rather than by season, the practical rule here is to learn the result by building rather than by month. Where tap rinsing consistently finishes clean, it will keep doing so; where it consistently spots, that is the Croton fraction and it will not improve — which makes a filtered final rinse a per-route decision, not a citywide policy.

The dominant residue in this city has nothing to do with the supply. A century of coal heating left soot embedded in masonry, and rain remobilises it onto the glass below cornices, lintels and sills. It is greasy rather than mineral, it needs a surfactant, and it reappears from the wall above after every heavy rain regardless of how well the glass was cleaned.

Access, not cleaning, is the business. Co-op and condo board approvals, certificate-of-insurance requirements, doorman and service-entrance scheduling, freight-elevator bookings and walk-up carries mean labour minutes per pane run two to three times a suburban job. Anyone pricing this market on pane count alone will lose money on every building with a lobby.

Pre-war glazing putty failure is endemic across the older stock, and it turns a routine clean into a liability question. On original steel casements and wood sash, hardened and cracked putty can release glass under pressure, so the first pass on an old building is an inspection and a conversation before it is a wash.

Rope access and suspended scaffold work on high-rise elevations is a regulated trade here in a way it is not in most of this site, with its own training, permitting and insurance regime. That is the ceiling on the market and it is a separate business rather than an extension of the residential one.

The building stock spans nearly two centuries inside a few blocks — cast-iron loft glazing in SoHo, pre-1900 brownstone wavy glass in Brooklyn, 1930s luxury co-op ornament on the Upper East Side, and post-2000 curtain wall in Long Island City. Method has to change by block rather than by neighbourhood.

Heavy road salting from December through March produces an aerosolized salt mist that bonds to ground-floor glass and corrodes aluminum and steel sash hardware over time. The salt film cleans off but the underlying frame damage is cumulative. Worst in NYC, Long Island, and the snow belt.

Pre-WWII NYC and inner-Westchester building stock still sheds a fine particulate that combines with airborne grime to produce the characteristic gray film on old brownstone and tenement windows. The film is not modern pollution alone — masonry chemistry and a century of coal-era residue are in the substrate.

The pre-1945 wood-sash housing stock in NYC, Westchester, and the older upstate cities is reaching the end of its original glazing putty service life. The putty crumbles around the perimeter of the pane and produces a chalky residue on the lower edge of the glass that cleaning does not solve. Documentation and a glazier referral are the right move.