Water leakage from pipeline damaged common area

Greetings !! I am the owner of a flat in Bangalore. I bought a flat 4 years ago . But for the last more than 1.5 years, we have seen seepage on the outside wall of our kitchen area but no damage or leakage inside our flat. Our kitchen and staircase walls are common. When we inform the association they have checked with the builder and as per the builder "water leakage is from the water pipeline inside the flat due to interior work and the owner has to repair it". We came to know about it only a few months ago but builder has sent a report to association long back. After many arguments with the association we started repairing work and we came to know that water leakage was due to a damaged pipeline used by the builder, nothing related to interior works. Builders have used damage pipelines (Water pipeline passes from inside of wall/Kitchen tiles). Apartment Staircase Common area is very badly damaged due to 1.5 year water leakage (approx 4 lower floors common area are damaged). Now the association is asking us to bear the repairing cost of all seepage. But leakage is due to bad material used by builders. It is not our fault. Who should bear the cost of repairing the common area and all flats which are damaged due to this leakage? When we informed the association about the leakage building was in DLP, but now it's DLP over. We already spent enough money to find the leak and repair it from inside our kitchen. Association also told us that if we don't repair it they will add it to our flat due maintenance and stop service of our apartment. Our society is register in Karnataka Apartment Association Ownership Rules, 1974). Please advise on it