Most of the times, as laymen, it never occurs to us to have a closer look at the walls and consequently we end up spending a lot to fix secondary issues due to seepage. Seepage on bathroom adjoining walls is very common. It could be because of seepage of water through the gap between drain and tiles or leakage of rain water through roof or cracks in the exterior wall. A thorough (visual or tactile) check of all the walls is a must before you decide to move in.