I can think of two notable jobs like this, both related to a fault on the tank in the loft.
One leaked into the master bedroom onto the bed, the bed got so heavy it ended up in the front room.
The other less damage but a good foot of water in the hall, neighbours spotted it leaking out the front door.
Both where away on holiday water had been running for days.
Also seen where a rat had chewed through a blue plastic main in the cavity where it entered the property, that made a mess.