The water heater in the garage
Regional building habits decide where the damage goes. In this part of the state the water heater lives in the attached garage or in an exterior closet, almost never in a basement. That single convention explains a large share of the residential water losses across Cerritos, Downey, Simi Valley and the post-war tracts generally.
Where the water goes when the tank fails
A tank does not usually burst. It corrodes through at the bottom and begins to release water steadily, often overnight. A garage floor slopes toward the door in theory; in practice it is loaded with stored belongings, and the water finds the shared wall with the house before it finds the driveway.
That shared wall is the problem. On the other side of it is usually carpeted living space — a bedroom, a hallway, a family room. Drywall wicks upward, carpet pad absorbs sideways, and by morning the wet edge is well into a room that has no visible water in it at all.
The pan, the drain and the thing most houses are missing
A drain pan under the tank is only useful if it is plumbed to somewhere. A great many installations here have a pan with no drain line, which catches the first litre and then overflows, or a drain line that terminates against the exterior wall where nobody would notice it discharging.
The temperature and pressure relief valve is the other component worth knowing about. When it discharges it is doing its job, but if its line ends inside the garage rather than outside, the result looks exactly like a tank failure and is diagnosed as one.
The laundry connection next to it
In the same garage, usually within a couple of metres, are the washing machine hoses. They fail differently — suddenly, under full pressure, and while nobody is home — and they produce far more water in an hour than a corroding tank does in a night. The two failures share a location and share a path into the house, which is why a garage that has flooded once tends to be worth looking at as a whole rather than one appliance at a time.