I once had a ceiling leak of water from my upstairs neighbor.  I called a contractor, and he broke open a segment of the ceiling where my vent was - and the entire gap between my unit and upstairs looked like something from Venus - terrifying colors&#x2F;growths taking place.  The contractor said that there was a massive mold infusion, and that we would need a hazardous material team to come clean it up, and we were looking at a bill of around $20,000 - $30,000 for the team to come do the full cleanup of the riser.<p>I freaked out a little, and thankfully had a calm property management company that just said, &quot;Look the area above bathrooms <i>always</i> looks like this, and we just need to have the people upstairs caulk a bit better around their bathtub, and we&#x27;ll be fine.<p>I&#x27;m not going to claim I have any idea whether calling the HazMat&#x2F;FireDepartment team makes sense here (Hell, Mercury is dangerous) - but it&#x27;s always a good idea to see if there are <i>safe</i> alternatives that might save you several tens of thousands of dollars.