The Inland Empire has a large stock of homes built between 1975 and 1995. Many of those homes used Schedule 40 PVC for interior supply lines and polybutylene for branch lines. PVC becomes brittle over decades and can crack suddenly under normal water pressure. Polybutylene — a gray plastic pipe widely recalled in the 1990s — deteriorates from the inside out.
The region's hard water is the second major factor. Riverside County water runs high in calcium and magnesium, depositing inside copper fittings and at soldered joints over time. A fitting that looks fine from the outside can have a nearly closed bore from scaling on the inside.
Temperatures in the Coachella Valley, Hemet, and the mountain passes above Banning can drop into the mid-20s on winter nights. Exposed supply lines in garages, crawlspaces, and exterior walls freeze, expand, and split — often silently overnight.