Alhambra is a mix of pre-war bungalows and later apartment construction, and the two produce different work. Older homes bring original plumbing; the apartment stock brings shared systems.
In multi-family the practical difficulty is rarely technical. It is access and authority, because the source is often in a unit or a common area that the affected resident cannot reach.
What goes wrong in Alhambra properties
Angle stops under sinks and toilets are a leading source across both. They are cheap, they are decades old in a lot of these buildings, and they fail without warning.
Older bungalows add cast iron drain lines that have reached the end of their service life. Those fail below the floor, which means the damage is done to the structure before it reaches anything visible.
Who is responsible when the leak is in a common area?
That depends on the building's documents rather than on where the water ended up. Report it to management immediately and photograph everything, because the determination is made on the record.
How long do angle stops last?
Longer than they should be trusted. If yours are original to an older building, replacing them is cheap and it removes one of the more common causes of a serious loss.