Independent proof from a neutral official
A housing, building, or health inspection can provide some of the strongest evidence a tenant can have, because it comes from a neutral government official who documents the problems officially.
When a code-enforcement or health inspector examines your unit and finds violations, their report is an independent, credible record that the conditions were real and serious — not just your say-so. Inspectors can also order the landlord to make repairs, which adds pressure to fix the problem, and their findings can support a rent-refund, defense, or damages claim later.
Because the inspector is a disinterested third party, their documentation is often harder for a landlord to dispute than a tenant's photos alone. It also creates an official date establishing when the violations were confirmed.
To benefit, you generally contact your local code-enforcement or health department to request an inspection, then keep a copy of any report and note any reference numbers. If an inspection could help document problems in your rental, understanding how to use it matters. A free, confidential review can help you understand how an inspection fits into building your case.
This is general information about California tenant rights, not legal advice. Every situation is different.