The single most common call we get is some version of the same sentence: the windows have just been cleaned and they still look bad. Almost every time, the glass is perfectly clean. What is left on it is mineral, and no amount of washing moves mineral, because washing was never the thing that was going to move it.
Here is what is actually happening. Water that lands on your glass is carrying dissolved calcium and magnesium — from a sprinkler head, from rain running off a stucco parapet or a tile roof above the window, or from ocean spray. The water evaporates. The minerals do not. They stay on the surface as a deposit, and the next time it happens they build on top of the last lot. What you end up looking at is not dirt sitting on the glass; it is a hard mineral layer bonded to it.
That is why a normal clean makes no difference, and it is also why the timing matters so much. In the first weeks the deposit sits on the surface and a proper hard-water treatment takes it straight off. Left for months it thickens and bonds harder. Left for years, glass is porous enough at a microscopic level that the minerals begin to etch into the surface itself — and at that point the marks are physically part of the glass. Restoration can sometimes polish that back, but it is slow, it costs real money, and on coated or tempered glass it is not always possible at all. Replacement is the honest answer more often than anyone wants to hear.
The pattern on the window usually tells you the source before we get there. A fan of spotting across the bottom third of a pane, heaviest at one corner, is a sprinkler head — the arc of the spray is drawn right on the glass. An even haze over a whole elevation facing the water is salt. Vertical streaking from the top edge down is run-off from whatever sits above the window, and that one gets worse every rain.
Prevention is genuinely simple and almost nobody does it. Turn the sprinklers that hit your glass so they do not, and check them after any gardener has adjusted a head, because that is when it starts again. Water the beds under windows early enough that the sun does not bake the spray onto the pane. If your property is ocean-front, put the glass on a schedule rather than waiting until it looks bad — by the time salt film looks bad it has been bonding for a season.
If you have spotting that has survived a clean, it is worth getting looked at sooner rather than at the next convenient moment. The difference between a treatment and a replacement is mostly a question of how long it has been sitting there.
Over the Top Window Cleaning treats hard-water spotting across the South Bay, Palos Verdes, the beach cities, Los Angeles, Malibu, Pasadena and out to Santa Barbara. Free written quotes — call (310) 972-8217.