Why spots form even on treated water
All tap water carries some dissolved minerals. When a droplet dries on glass, the water leaves and the minerals stay. Miami's heat and humidity mean a shower stays wet longer, and the outdoor sun bakes spots onto car windows and patio doors after the sprinklers run.
WASD's source is the Biscayne Aquifer, a limestone formation, so the raw water is mineral-rich. The utility addresses that at the plant: its 2024 Water Quality Report describes lime treatment at the Alexander Orr, Jr. plant and enhanced softening at the John E. Preston plant.
Spots vs. scale: what you are seeing
- Spots on glass and dishes: evaporation residue. Can appear even with moderate hardness.
- Crust on aerators and shower heads: scale building up where water flows and dries repeatedly.
- Scale inside kettles and the water heater: minerals that come out of solution when water is heated.
- Orange or brown marks: usually iron, not hardness. See orange and rust stains in Miami.
North or south of SW 8 Street
WASD's report says homes north of SW 8 Street are generally served by the Hialeah and Preston plants and homes south of it by the Orr plant. Each plant softens differently, which is one reason neighbors across town can see different amounts of spotting. Your own tap is the only measurement that counts.
Softener or conditioner?
| Ion-exchange softener | Salt-free conditioner | |
|---|---|---|
| What it does | Removes calcium and magnesium | Changes how minerals behave so less scale sticks |
| Spots on glass | Reduced, because minerals are removed | Minerals still present, so spots can still form |
| Needs | Salt, drain, outlet | No salt or drain |
Living Water installs ion-exchange softeners. More detail in salt-free conditioner vs. ion-exchange softener.
Simple steps while you decide
- Squeegee shower glass after each use.
- Soak aerators and shower heads in vinegar to loosen crust.
- Water early in the morning so sprinkler spray on windows dries less harshly.
- Run the dishwasher with a rinse aid and pull glasses out promptly.
- Check whether your sprinklers run on an irrigation well; untreated well water spots glass much faster than city water.
- Book a free hardness test: call, text or WhatsApp Jorge at (305) 793-5974.
Updated 2026-10-17 · Living Waters · Jorge Canela, Water Quality Specialist