To prevent mold due to water leakage, you need to do annual roof inspections after 5 years. To mitigate and remove the mold, you need to determine how much of an area in each unit will be affected. If a bathroom or a kitchen has to be upset, then the tenant needs to move out for the work to be completed because they will not have normal living quarters. If there are small areas in each unit and you can contain them, that’s fine. If the water damage is throughout the apartment, you have to look at it on a case-by-case basis. You will need to first dry out the materials so the salvageable materials can be sanded cleanly of the mold. You will need to remove drywall or plaster that is water damaged and not reusable, 6-12 inches beyond where the water damaged ends. After it is deemed to be cleaned by the remediation contractor after at least 24-48 hours, the inspector should come back and inspect each area to make sure it is visibly clean and dry. If it meets that criteria then an air sample should be taken in each containment to determine that the mold spores are at an acceptable level, which has to be less than 2 spores of any mold.