seeking guidance rental property water damage

[Darryl Lew]

Hi everyone,

seeking assistance on the following matter:
I stay in a high-rise apartment in New Jersey. In the month of July'17, there was shower clogging in my bathroom which resulted in water overflow. We seen that the water did not travel from shower area -> bathroom floor -> living room but it happened internally beneath the walls / floor to the living room. There was water damage to the parquet wooden floor in the living room where the tiles had buckling but returned back to original state in 2-3 weeks. Management for the building came in and fixed the shower area clogging saying that shower clogging is our responsibility. Now per recent checks from a repair company there is mold on the living room floor and needs to be replaced to the amount for $12000 for which the landlord is holding us responsible.
We have repeatedly told the landlord that shower clogging may be our responsibility, but the subsequent damage to the living room floor tiles is more of a construction defect that allowed water to travel internally and cause the damage. Landlord disagrees and says he has a legal right to hold us responsible for the damage and that we will have to pay for it

Please provide me some guidance how to go about this issue.
- What are my rights in this matter? How do I prove that the water has traveled internally due to some defect and not traveled from the bathroom floor onto living room?