I have yellowish/brownish water stains appeared suddenly in the living room ceiling. I discovered it in the morning on 2/17 (Wed) after the rigid cold day (-22 degree) on 2/14 (Sun), snow storm on 2/15 (Mon) and a warm day (48 degree) on 2/16 (Tue). The water stain is a line 7 feet long and width is 7 inches. Another water stain is 4 feet long and width is about 7 inches. The 3rd water stain is about 5 feet long and width is about 7 inches. They connect with each other like a U shape. The U shape water stain appeared all at once suddenly on the living room ceiling, just right up the ceiling is the bathroom. I called plumbers and finally had a plumber called me back after a few days. I did not use the bathroom while I was waiting for plumbers' reply. The plumber asked me to used the toilet one day, shower on 2nd day & 2 water sinks on 3rd day to find out where is the water leak. I follow instructions and cannot find any water leaking and the stain stays the same shape, not getting worse. I have walk up attic and I can't any water leaking in the attic ceiling, floor and even no water stain on the 2/F ceiling. I checked the vent pipe on the attic (which is go through to the roof) and I touched the pipe, cannot find any wet when it was on a rainy day. I don't think it is condensation becasue my water pipe is CPVC not copper. Besides, my living room and 2nd floor temperature will be lower than 65 degree, so I should not have frozen pipe that will condensation happend. No clue why the water stain appeared and how the water comes to the living room ceiling. I am afraid the mold and something happpened inside the ceiling that I don't know. Hope some experts can help to find out the clue.
For more infomation, I don't use that bathroom much. On 2/12 (Fri), the town had to fix the fire hydrate just opposite to my house, the town shut down the water and I had no water came in until 3 pm on that day. I started to use water in the kitchen in the evening, the water was very brown color. I also checked the bathroom, it had brown water too. I switched on the water tap and kept the water running until clear only in the kitchen. I did not use the bathroom since then, I don't know whether it has relation with the water stain.
Thank you in advance.