Cal. Civ. Code § 43-32-8

In every hiring of residential premises, whether in writing or parol, the lessor shall keep the premises and all common areas in reasonable repair and fit for human habitation and in good and safe working order during the term of the lease except when the disrepair has been caused by the negligent, willful or malicious conduct of the lessee or a person under his direction or control. The lessor shall maintain in good and safe working order and condition all electrical, plumbing, or heating systems of the premises, except when the disrepair has been caused by the negligent, willful or malicious conduct of the lessee or a person under his direction or control.
The parties to a lease or hiring of residential premises may not waive or modify the requirements imposed by this section; however, the lessor may agree with the lessee that the lessee shall perform specified repairs or maintenance in lieu of rent.
The provisions of this section shall be in addition to any covenants or conditions imposed by law or ordinance or by the terms of the lease. Nothing in this section shall be construed to alter the liability of the lessor or lessee of residential premises for injury to third parties.