The answer to 'roof vent water stains' is that they are typically caused by leaks around the roof vent or improper installation. Symptoms include water stains, mold, or moisture buildup around the vent. Solutions may include resealing the vent, replacing damaged flashing, or ensuring proper ventilation.
If the issue is minor, such as a loose vent or dried-out sealant, you may be able to fix it yourself. However, for more complex problems like structural damage or persistent leaks, it's best to call a professional roofer to properly diagnose and repair the issue.