What the spots actually are
When mineral-rich water evaporates, it leaves calcium and magnesium behind. Early on that deposit sits on the surface and comes off with the right cleaner. Over months and years it bonds and begins to etch into the glass or stone, and at that point cleaning alone will not restore clarity.
Windows and shower glass
The single most useful fix is free: adjust the sprinklers so they stop hitting the glass. After that, squeegee shower glass after use and keep exterior glass on a regular cleaning schedule so deposits never get the chance to bond.
Heavily spotted glass sometimes needs a mineral-specific treatment and, in severe cases, professional restoration or replacement. That is why catching it early is worth so much.
Tile, grout, and stone
On tile and grout, mineral film traps soap residue and turns into the chalky haze common in local showers. On marble and travertine, the wrong cleaner makes it worse — anything acidic etches the stone permanently.
Use pH-neutral cleaners on stone, keep it sealed, and have polishing done when the surface has lost its reflection rather than scrubbing harder.
What to avoid
Skip vinegar, lemon, bleach-based scrubs, and abrasive pads on natural stone and older glazed tile. They may lift the film once and cost you the finish permanently.