Building a strong record of the infestation
You prove a rodent infestation with documentation: dated photos and videos of droppings, gnaw marks, nests, or the rodents themselves; written reports to your landlord; any pest-control records; and receipts for damaged food or belongings.
Build the record over time. Photograph droppings along baseboards and in cabinets, chewed packaging and wiring, and any rodents you catch or see. Save every text and email with your landlord, since these show what the landlord knew and when. If an exterminator visited, keep the service records, which can confirm both the infestation and how it was handled.
Even a recording of the scratching sounds in the walls at night can help, along with notes about thrown-out food and disrupted sleep. You do not need a laboratory to have proof; a consistent, dated record usually tells the story. A free review can help you understand which evidence matters most in your situation.
This is general information about California tenant rights, not legal advice. Every situation is different.