The answer to 'why is my metal roof water stains' is that water stains on a metal roof are typically caused by poor drainage, condensation, or mineral buildup. Metal roofs can develop water stains if the roof isn't properly sealed, if there are gaps or holes allowing water intrusion, or if the roof isn't angled properly for adequate drainage. Stains may also be caused by minerals in the water reacting with the metal.
To fix water stains on a metal roof, you'll first need to identify the underlying cause. Check for proper roof slope, seal any gaps or holes, and clean the roof to remove any mineral buildup. In some cases, you may need to have the roof professionally inspected and repaired. Attempting DIY fixes on a metal roof can be risky, so it's usually best to call in a professional roofing contractor.