In evaporation, only the water molecules vaporize. The contaminants are left behind. That’s why “distilled” water is pure. Rain starts from the same process. Rain can pick up other things already in the atmosphere like CO2, making it slightly acidic, or sulfur and particulates already airborne, but it starts out pure. Metal particles just don’t stay airborne for long.
I do know that but suffered a bout of temporary (hopefully) stupid. That’s why I let the steam buildup up on my shower plexiglass divider, rather than splashing shower head water on it before squeegeeing off. No water spots from minerals.