The short answer
Hard water stains are mineral deposits left when water evaporates on glass, most often from irrigation overspray. Stop the water at the source, clean often enough that minerals never bond, and restore glass that has already etched.
Where it comes from
- Irrigation overspray: the most common cause, often in a telltale sprinkler pattern
- Runoff from precast concrete and masonry above the glass
- Acid rain and pollution
- Oxidation running off metal window frames
Prevention, in order of impact
- Fix the source. Re-aim or adjust sprinkler heads so they stop hitting the glass, and check after landscaping changes.
- Tighten the cadence on exposed elevations so deposits are removed before they bond.
- Add hard-water removal to the scope where overspray cannot be fully stopped.
- Consider protective treatments after restoration. See what protective coatings prevent and what they don't.
Remediation by stage
| Stage | What you see | Remediation |
|---|---|---|
| Fresh deposits | Spots that clean off | Routine cleaning |
| Bonding | Spots that routine cleaning will not lift | Hard-water removal |
| Etched | A haze that never clears | Glass restoration |
| Deep etching | Pitting that cannot be removed without distortion | Replacement |
Coated glass needs extra care: acidic cleaners are not recommended on coated glass, so identify any exposed coating first.
Why speed matters
Each stage costs more than the last, and the final stage is a capital expense. See the hidden cost of neglected commercial glass and hard water and mineral staining: cleaning vs. restoration.
Not sure what you are looking at? Use the glass and metal damage triage guide, read the full Facade, Glass, and Metal Restoration guide, or have our team assess the surface and recommend the right approach, in writing.
