How quickly the landlord must respond
A California landlord must fix a plumbing problem within a reasonable time after being notified, and serious problems — no water, no hot water, or a major leak — should be handled quickly, sometimes within a day or two.
There is no single deadline in the law, but "reasonable" depends on how serious the problem is. A total loss of water or hot water, a burst pipe, or a backed-up drain is urgent and should prompt a fast response, even outside normal hours. A minor drip may fairly allow a bit more time, though it should still be repaired.
Reporting the problem in writing and keeping copies helps establish exactly when the landlord's clock started. Note each report and any follow-ups. If your landlord lets a serious plumbing problem drag on well past a reasonable time, a free review can help you understand your options.
This is general information about California tenant rights, not legal advice. Every situation is different.