Legal Question in Landlord & Tenant Law in California

Flooding and mold are habitability issues. The landlord is obligated to properly remediate those problems. You need to write a polite but firm letter advising him of these obligations. If he doesn't respond, you may consider having a remediation company come to the house to give an estimate of what repairs need to be done and there cost and send that to your landlord in a follow up letter advising that you will have the work done and withhold rent if they refuse to fix the problem.