1. if you have a single handle shower control, there is a large circular metal plate on the wall. Water can leak between the plate and wall and runs to the inside of the wall, and ended up on the floor.
2. Same if you have a tub spigot; water can seep through the gap betweeen the plate and the wall.
The above two should be visible if you look closely at the seal between the plates and wall.
3. the tub drain is not tightened or the seal aged and starts to fail (this does not happen a lot, but happens)
