We have had a very slow leak that has caused the basement plaster and lath ceiling to bubble in several places. The leak is so slow that we have never seen water, just the slow but consistent damage it is causing. As I said above, the water has cause bubbles in the ceiling and is now causing some bowing of the sheet rock wall. We cut open the ceiling in a futile attempt to determine from where the moisture is coming. Any suggestion is appreciated. Thanks.