The plumbing a livable home requires
A California landlord must maintain the plumbing that makes a home livable: working pipes and drains, hot and cold running water, functioning toilets and sinks, a working water heater, and safe gas plumbing where it is provided.
State law requires plumbing kept in good working order and connected to proper water and sewage systems, along with hot and cold running water and, where applicable, gas facilities in good repair. In plain terms, the water should run, drain, and heat properly, and the fixtures should work.
Just as important, the landlord has to keep all of this functioning throughout your tenancy — not only on the day you move in. A system that was fine at move-in but fails later is still the landlord's to repair. If your landlord is neglecting basic plumbing your home depends on, a free review can help you understand your rights.
This is general information about California tenant rights, not legal advice. Every situation is different.