Why Pure Water Changes the Result
Ordinary tap water carries dissolved minerals. Spray it on glass, let it evaporate, and those minerals stay behind as spots. Run water through filtration and deionization and you strip those minerals out. The water becomes aggressive at picking up dirt and, critically, it dries with nothing left to deposit. A soft brush on a carbon fiber pole agitates the frame and glass, the pure water rinse carries it away, and the pane dries clear with no squeegee touching it. Exterior glass gets cleaned from the ground, so nothing leans on the sill or the flashing.
Main Line Glass Types
True divided lite windows on pre-1940 Haverford, Wynnewood and Narberth homes have many small panes, real muntins, often original glass with visible waves — slow work by definition. Exterior storm windows are common on Ardmore twins and Narberth Victorians — there are three surfaces per opening, not two, and the space between storm and sash is usually the dirtiest part. Large fixed picture glass in 2000s Malvern and Blue Bell construction is the panes most prone to visible streaking.
Hard Water Spots Are a Different Job
If a lawn sprinkler head has been hitting the same window for two summers, that is not dirt. Mineral deposits bond to the glass surface and no amount of washing removes them. They need a dedicated restoration step with an abrasive-free mineral treatment, and severe cases etch the glass permanently. The fix that matters is redirecting the sprinkler head.
By Town
Ardmore (19003): twins, storm windows, no ladder ground on the party-wall side. Narberth (19072): painted Victorian frame, true divided lite, the tightest lots in our area. Wynnewood (19096): 1920s to 1950s stone and brick, original wood sash, canopy-shaded north glass. Haverford (19041): estate scale, high pane counts, tree-obstructed access. Gladwyne (19035): sloping wooded lots and outbuildings with their own glass. Conshohocken (19428): hillside elevations and river humidity. Paoli (19301): 1890s wood sash, postwar aluminum frames, and 2000s vinyl, often on one street. Malvern (19355): large modern window walls in the townships, historic sash in the borough. Newtown Square (19073): big open elevations, often paired with patio washing. Blue Bell (19422): full-sun lots where spotting from irrigation is the most common complaint.