In December of last year my wife was in the bath when I used the restroom downstairs from her. I looked up and noticed that above the toilet some of the paint had separated at the edge of the wall and ceiling.
I poked one finger up, and surprisingly, through the ceiling and a cup or two of water just fell through the hole.
This affected my goals in several ways. First, there was an increased safety risk due to cutting drywall overhead. Second, I had to spend time to figure out where the water came from and fix it. Third, I had to spend money to solve the problem once I figured out what was going on.
Since I didn’t want this problem to happen again, I decided to trace the causes as far as I could. Unfortunately, that was not very far.
There ended up being two water leaks. Once large leak came from a dry-rotted seal on the bathtub overflow. A second, smaller leak came from a loose union fitting on the drain piping.
Why was the union fitting loose? Since I don’t know who installed it, I certainly can’t ask them about the job. I could speculate about the many reasons why the union fitting wasn’t properly tightened, or why it became loose over time, but that would not be good RCA practice.
Why did the overflow seal leak? Because it was dry rotted. Why was it dry rotted? Because it was installed without caulk. Why was it installed without caulk? Again, we don’t know. There’s no one available who can answer that question.
In the end, this RCA attempt left me with nothing more than fixing the immediate problem and the most superficial possible insight into why one of the parts failed.
Better that than to speculate.
How would you approach the investigation at this point?