Last friday AM I found a big pool of water in our basement; coming from the ceiling where there are no water pipes in the area. I pulled out a few of the water logged ceiling tiles and the wood beams were soaked. We checked both 1st and 2nd floor bathrooms but saw nothing. Turned off the water at the main pipe. We headed out of town for a pre arranged trip.We were thinking the water was following a beam or board down. Our daughter checked the basement the next day no water anywhere. On Sunday pm we returned and turned the water back on. no leak. checked during the night, no leak. Since then no water leaking. The soil level is lower then the ceiling so not from the outside. We are just waiting for the return altho we have not flushed the 2nd floor toilet. All we could imagine was tearing out walls and floors "looking" for a source. House was built in 1944.
No source for ceiling leak?
Good luck - old houses can be a real challenge when issues occur.
Even if the problem water is from 2nd floor commode (or sink or tub?), it may take a while to follow the path since it has had time to dry.
Maybe the waterstain on the joists or beams will give you a hint about the direction of travel.
Some demolition will be inevitable, but hopefully not too much.
Even new houses can have leaks. Our second story shower had a serious leak. Despite having two plumbers look at it and their attempts at diagnosing the problem, the leak was there the next time we had overnight guests. It appeared the leak was from showering and not bathing. Grandkids taking a bath seemed to be okay but adults taking showers meant serious leaks in the laundry room and kitchen below the bathroom and then into the basement.
Finally took the tub faucet off to observe any leaks. When the water flow was plugged with my finger (to divert the flow to the showerhead), it leaked pretty bad. Luckily I also saw that it dripped even when running a bath. It turned out to be the solder joint at the elbow. I had to cut a hole in the wall on the other side of the tub and sweat a new elbow on the existing pipe. No fun but at least the mystery leak was fixed. I almost bought a borescope so I could see what was going on inside the wall without tearing the whole wall down until I saw where the leak was coming from.