The oldest houses in the valley
Newhall is where the Santa Clarita Valley started. The town grew up around the railroad from 1876, and the streets around Old Town carry housing that predates the rest of the valley by decades — including a good deal of it built long before copper was the normal thing to put in a wall.
Age is the whole story here. Galvanised steel supply lines corrode from the inside out, so they announce themselves as brown water and falling pressure years before anything actually drips. Cast-iron drain stacks crack and run slow. Neither is a patch job, and on a house of this vintage it is worth finding out which one you have before spending money on the symptom.