Galvanized steel supply pipe was standard residential practice from roughly the 1920s through the 1950s, and Old Town Placentia is squarely in that band.
Galvanized fails from the inside out. Mineral and rust deposits build up on the pipe wall, restricting flow and increasing turbulence, and the wall thins from within until it splits or weeps. The warning signs arrive years ahead of the failure: rust-tinted water when a tap has stood overnight, pressure that has quietly declined, and visible corrosion crusting at threaded joints. Most homeowners get used to all three and never connect them to a coming burst.
These older houses also have wall assemblies that behave differently. Lath and plaster does not dry like drywall — it holds water in the brown coat and behind the lath, and drying it needs patience and readings rather than the standard playbook. And where a wall has been opened before, you will often find a partial repipe: newer copper for part of the run, original galvanized beyond it, with the failure right at the dissimilar-metal joint.
North and east of the core, Alta Vista and the 1960s tracts have the familiar slab-on-grade profile — hard water pinholes and clay soil movement, with original systems now well into replacement age.