Who pays to restore hot water
No. In California, providing hot water and maintaining the water heater are the landlord's responsibility, so you generally should not have to pay to repair a water heater or restore hot water — unless you clearly caused the damage.
The cost of fixing or replacing a failed water heater, or repairing the plumbing that carries hot water, falls on the landlord as part of keeping the rental livable. A tenant might be responsible only if they damaged the equipment through clear misuse.
If a landlord tries to charge you for a repair that is really their duty, or asks you to buy your own water heater, that is worth questioning before you agree or pay. Keep any communications about who is responsible. If your landlord is pushing hot-water repair costs onto you, a free review can help you understand what is fair.
This is general information about California tenant rights, not legal advice. Every situation is different.