Who repairs broken plumbing fixtures
The landlord is generally responsible for repairing broken faucets, sinks, toilets, and other plumbing fixtures, because keeping the plumbing in working order is part of maintaining a livable home.
When a faucet leaks or will not run, a sink will not drain, or a toilet will not flush or fill, those are usually the landlord's to repair. A tenant might be responsible only if they broke the fixture through misuse. Ordinary wear and everyday failures are the landlord's job, not the tenant's.
Report the problem in writing, and if a leaking fixture is also causing water to pool or seep, note that too, since it can grow into a bigger issue like water damage or mold. If your landlord ignores a broken plumbing fixture, a free review can help you understand your options.
This is general information about California tenant rights, not legal advice. Every situation is different.